Like Dean, Sam calls Castiel by the nickname "Cass".
Castiel and Sam didn't meet for a while, but they are both aware of each other's existence. Sam hears about Castiel from Dean while Castiel knew about Sam, and the fact that Sam was using his powers to exorcise demons with his mind. Sam wanted to meet Castiel, mainly because he wants to thank the angel who rescued his brother out of hell. The two do finally meet face to face in It's the Great Pumpkin, Sam Winchester.
During Metamorphosis, Sam is made aware that Castiel told Dean about his continued use of his powers.
|“||Sam Winchester. The boy with the demon blood. Glad to hear you've... ceased your extracurricular activities.||”|
— Castiel to Sam
in It's the Great Pumpkin, Sam Winchester
Sam and Castiel finally meet in It's the Great Pumpkin, Sam Winchester when Sam notices people in their motel room, he pulls a gun, but is stopped by Dean. Dean introduces Castiel to Sam. Sam stammers and offers Castiel his hand in greeting, saying it was an honor to meet the angel who raised his brother from hell. Castiel looks at Sam's hand, unsure what do with it. Castiel does take Sam's hand and shakes in greeting. Castiel expresses the fact that he's glad Sam has stopped using his powers.
Then the angels reveal they plan to destroy the town, and Sam (as well as Dean) doesn't like this plan at all. Sam tries to talk the angels out of it by saying they can stop the witch before she summons a very powerful Demon. Castiel tells Sam and Dean they have their orders. Sam asks them if angels are supposed to show mercy. After Dean's pleas, Castiel then gives Sam and Dean permission to stop the witches.
They meet again in Heaven and Hell, when Castiel comes for Anna Milton. Sam asks Castiel why they would want to kill an innocent girl. Castiel responds by saying that Anna is far from innocent. Sam is confused by this. Uriel attacks when they continue refusing to give Anna to the angels. Sam asks Castiel to stop this, while calling him "Cass" but Castiel merely knocks Sam out with a touch and heads to where Anna is. Then, Castiel and Uriel are sent away by Anna. Because of what Castiel tells Sam, Sam starts to investigate Anna.
In On The Head Of A Pin, Sam saved Castiel from Alastair when the latter was about to banish him to Heaven as Castiel was amazed by Sam's power when he killed the demon. Afterwards, Castiel comes to Dean's hospital, where Sam is sitting beside his brother's bedside. Sam demands Castiel get in there and heal Dean. Castiel tells Sam he can't. Sam argues that Castiel and Uriel are the ones who put Dean in there, all because they can't keep a simple devil's trap together. Castiel apologizes to Sam, unable to explain what happened. Sam snaps at Castiel, saying that making Dean torture again was for nothing. It's not the demons, but something else. Castiel brings up the possibility that Alastair was lying, but Sam shoots it down. Castiel believes Sam is right about this and finds it was Uriel who is killed by Anna.
During The Rapture, they saw each other again and Castiel was disgusted to see Sam consuming demon blood and using his powers.
In When the Levee Breaks, it is Castiel who lets Sam out of the panic room. Castiel also aids Dean to get to Sam, so Dean can stop the breaking of the final seal.
In Lucifer Rising, Castiel was on the angels' side and stopped Dean from trying to contact Sam. Castiel soon rebelled to help Dean in stopping Sam from killing Lilith, who was the last seal to Lucifer's Cage. However, the attempt was a failure.
In this season, Castiel has rebelled against Heaven and now sides with the Winchesters. Sam and Castiel's friendship really develops and Sam starts to address Castiel as Cass just like Dean does.
|“||The answer is still no, because Sam is my friend.||”|
in The Song Remains the Same
Castiel was killed by Raphael off-screen, Sam was saddened at the death of his friend before it turns out Castiel has been resurrected by and rebelled against heaven and returns in Sympathy for the Devil and saves Sam and Dean from Zachariah. Castiel forces his brother to put the boys "back together" and leave. After Zachariah complied, Castiel brands Sam's (and Dean's) ribs with Enochian sigils so no angel (including himself), can find them. Before Castiel leaves, Sam asks him how is he alive. Castiel disappears before giving them an answer.
In I Believe The Children Are Our Future, Castiel shoots downs Sam's plan to talk to Jesse Turner about what's happening to him. Sam argues that once Jesse knows the truth, he will stop hurting people. Castiel points out that Sam didn't, and leaves. This comments hurts Sam (due to his guilt about drinking demon blood).
During Changing Channels, Castiel appeared to the Winchesters in the television world and stated he searched for Sam and Dean while they were dealing with The Trickster. Sam was worried when Castiel was teleported by the latter. When Castiel returned battered and bloodied, Sam questioned him on his condition as Castiel tried to warn him about the threat. After the trickster appeared, he flung Castiel away and banished him once he greeted him and Sam was angry at this though noticed the trickster knew Cass. When he and Dean got fooled by the trickster, Sam realized Castiel's warning and the trickster's familiarity was a sign that the latter was angel. After their suspicions were confirmed with the trickster being the archangel Gabriel, Sam watched as Dean forced Gabriel to bring Castiel back after threatening to pour holy oil on him when he was trapped in a ring of holy fire. Gabriel complied and Sam was relieved when Castiel confirmed he was fine.
In The Song Remains the Same, Castiel refuses to let Anna kill Sam, even declaring that he was his friend as Anna acknowledged his new change towards the brothers. Sam looked to Castiel to see if Anna's plan would work, though Castiel disagreed. Castiel also allowed Sam and Dean to time travel with him to save their parents from the rogue angel. Sam was worried at the pain it caused Cass and let him rest. At the end, Anna is killed by Michael and the Winchesters are returned to their time. Sam once again helps Cass after he returns to present in his weakened state.
When Sam and Dean go to Heaven in Dark Side of the Moon, Castiel asks them to look for Joshua, as he may know where God is. They find Joshua and find out that God had help them before by saving them and resurrecting Cass as well learning he knows about Earth's problems but simply doesn't feel he should get involved. This revelation hurts Castiel, who renounces his faith in God and disappears.
When Sam figures something is not right in a town, he calls Castiel in for help (99 Problems). When Castiel shows up drunk, he tells Sam he finds his voice grating. Sam is shocked after he notices Castiel is drunk and asks what happened to Castiel. Castiel answers he found a liquor store and "drank it". Sam attempts to help Castiel from wobbling, and asks if he's okay. Castiel leans over and tells Sam not to ask stupid questions. Sam tells Castiel about the demon attacks around town and the "prophet" Leah Gideon. Castiel tells Sam that she is no prophet (because all the names of the prophets are seared into Castiel's brain), and then Sam asks then what Leah is. Castiel later reveal that "Leah" is actually the Whore of Babylon. When Castiel brings a weapon to kill her, he tells them that only a true servant of God can use it to kill her. Castiel continues on by saying he can't do it, and, neither can Sam since he's an abomination (because of the demon blood). Sam looks slightly hurt, but understands.
When Dean decides to say 'yes' to Michael in Point of No Return, Sam brings Castiel along to help him stop Dean. Castiel uses his powers to send Dean to Bobby's house. Like Sam, Castiel is angry at Dean for giving up, so they both work together to make sure Dean doesn't leave Bobby's. Castiel also agrees with Sam questions about the angels' change in mind to Adam Milligan (the Winchesters' half-brother). When Dean does escape, Castiel brings Dean back unconscious. Sam asks Castiel what happened and Castiel answers "Me". Later on, Sam decides to bring Dean along on a mission to save Adam, despite Castiel not wanting to Dean to come along. Castiel can't understand Sam's blind faith in Dean.
As the final showdown comes along, Castiel comes once again to aid the Winchesters. In Two Minutes to Midnight, Sam is relieved to hear Cass is alright from his banishment and Castiel saves Sam from being tortured by Pestilence. Later on, Cass goes over Sam's plan to defeat Lucifer but warns him of the repercussions should he fail. Castiel later rescues Sam from being strangled to death by a zombie. Castiel is amazed how useful guns can be. Then in Swan Song, Castiel says an awkward goodbye to Sam, as Sam prepares to have an internal battle with Lucifer in his head.
After Sam trapped Lucifer and Michael into hell (at the cost of himself), Castiel who was resurrected and promoted to Seraphim used his new powers to successfully raise Sam from Lucifer's cage. Unfortunately, Sam's soul was left in the cage.
After Sam returned from Hell, he called Castiel many times for on how he returned, but Castiel never answered him, so Sam stopped calling.
|“|| Sam, it's so good to see you alive."|
"Yeah, you, too. Um, look, I would hug you, but--"
"That would be awkward.
In Family Matters, Castiel is trying to figure out what is wrong with Sam. Castiel starts asking Sam questions, and finishes with asking how Sam feels emotionally. Sam answers he doesn't know. Castiel tries to feel Sam's soul, only to find out Sam doesn't have one. Sam looks shocked at this discovery. Castiel tells Dean whoever brought Sam back, left his soul behind. When Dean asks if "Sam" is still even Sam, Castiel answers that it is an interesting philosophical question.
Castiel continues to help in the quest for Sam's soul in Caged Heat. Although he doesn't come right away. Sam tricks Castiel into coming down and calls Castiel an idiot for believing his lie. Sam asks Castiel to help, but Castiel refuses (due to the civil war). Sam continues by saying Castiel owes him and if Castiel doesn't help, Sam will find a way to kill Castiel (pointing out the extra time to do so since Soulless Sam doesn't sleep). Castiel is not fazed even daring him to try in a threatening way but he agrees to help. Later on, Castiel seemingly threatens Crowley to get Sam's soul back, but when Crowley says he can't, Castiel toasts Crowley's bones. Castiel reassures Sam they will find another way to get Sam's soul back.
In Like A Virgin, Sam now has his soul back and Dean calls Castiel to check on Sam. Castiel tells Dean that Sam's soul felt like it had been skinned alive. Later on in the episode, Sam awakes and recalls Castiel being killed while Lucifer possessed him but Dean and Bobby tell him he was resurrected, to his relief. Sam calls Castiel and he appears while telling Sam its good to see him alive and attempts to hug Sam (who sits down to avoid it). Sam tells Castiel he would hug Castiel, but it would be awkward. Sam goes on to talk about how its been a crazy year and how he just talked to Bobby about it. Castiel tells Sam he's surprised Sam even survived. Castiel asks Sam how it feels as Sam looks confused. Castiel explains, "to have your soul back". Sam is shocked to hear this news and plays along so he can get more details from Castiel about what really happened. Sam then learns from the angel that he returned from the cage but without his soul for a full year.
|“||Castiel: Sam, I am the one who raised you from perdition!||”|
After hunting Eve down, Sam (plus Bobby) begin to have suspicions about Castiel. Sam starts not to trust Castiel, and believes him to be working with Crowley (The Man Who Would Be King). Castiel still protects Sam and Dean despite these doubts. Then when Castiel's betrayal comes to light, they trap Castiel in a ring of holy fire. In there, Castiel tries to maintain his loyalty to them even revealing that he was the one who brought Sam back from the cage. Though surprised, Sam asks Castiel if he meant to bring Sam back soulless. Castiel tells Sam he didn't mean to (he didn't even know until Family Matters).
Despite Castiel's betrayal, Sam wants to call and does call Castiel for help in Let It Bleed. Although Castiel doesn't show himself, he answers Sam's prayer. Then Castiel does the unthinkable in The Man Who Knew Too Much. In order to detour Dean, he breaks down the wall inside Sam's mind and Sam goes into a coma. Castiel says he'll save Sam, only if they back off. Sam does wake from his coma, and comes to Dean's rescue. Sam stabs Castiel only to find out that Angel Blade doesn't work on him.
|“|| Dean, look, I know you think that Cass is gone."|
"Cause he is"
"He's not. He's in there somewhere, Dean. I know it."
— Sam and Dean about Castiel
in Meet The New Boss
Even after Castiel tore down his wall, Sam still believes that they can reach him. Despite Dean thinking Castiel won't listen, Sam calls Castiel, and tells him they can help. Although Castiel doesn't answer right away, he comes to Sam's call and asks for help. Sam sets out with the others to help Castiel.
The last moment they have together is when Castiel tells Sam where to find the blood cocktail meant to open Purgatory. Later, Castiel is overcome by the Leviathans, and Sam watches Castiel disappear into the water.
In The Born-Again Identity, Castiel comes to Sam's rescue as a demon attempts to fry Sam's brain. Castiel attempts to right his wrong by attempting to fix Sam's mental state, but fails. Castiel deeply regrets what he did to Sam, and he states that he can't fix it. Then the idea hits Castiel to switch places with Sam's mental state. Castiel takes on Sam's insanity, and begins to see Lucifer. Now sane, Sam is shocked to see Castiel alive, and becomes worried about how he's acting. Sam is a bit shocked that Dean wants to leave Castiel in the mental institution.
In Reading Is Fundamental, Sam thanks Castiel for helping him and taking on his hell. Sam promises to help find a cure for what Castiel took on. Castiel tells Sam that he doesn't need to fix anything and that taking on Sam's pain gave him purpose. Castiel also mentions that he doesn't see Lucifer anymore since it was Sam's own hallucination. Sam is sad to hear Castiel doesn't think that he's broken.
Sam inquired about what happened to Castiel in Purgatory, but got no answer from Dean. Sam is excited to see Castiel's return and he has regained his sanity. Sam is less suspicious of Castiel than Dean.
In Hunteri Heroici, Sam and Castiel make a connection when Sam is talking about living in a dream. When Castiel brings himself and Sam into the mind of Fred Jones, Castiel can relate to Sam, as he too, has been running from his problems, and makes a decision to return to Heaven, but is shot down by Naomi.
In Clip Show, when Castiel's relationship with Dean is strained due to Dean's anger over Castiel's lack of trust in him, Sam comforts Castiel, trying to convince him that Dean just needs time.
In "I Think I'm Gonna Like It Here," Castiel agrees to stop helping Hael in order to come and save Sam when he's dying. He also gives Dean his approval of Ezekiel helping, saying Ezekiel is a good soldier and indicating they are friends.
In "I'm No Angel," When Castiel is being tortured by the Reaper possessing April Kelly, Sam comes to his rescue with Dean though Castiel is briefly killed but resurrected by "Ezekiel". Afterwards, Castiel is excited by the idea of Sam and Dean being his guides to being human, but Dean is forced to ask him to leave to save Sam who "Ezekiel" threatens to leave and let Sam die if Castiel doesn't go.
In "Holy Terror," Castiel works a case of angel deaths with Sam and Dean, but "Ezekiel" once again forces Dean to send him away. However, this time, Dean partially explains why to Castiel who continues investigating on his own. After learning from Malachi that Ezekiel is dead, Castiel escapes and calls Dean to warn him that the angel who helped Sam isn't really Ezekiel. Unfortunately, his warning comes too late.
In "Road Trip", after the angel possessing Sam kills Kevin and takes off, Castiel comes to aid Dean with saving him. While Dean is originally going to kill Sam to kill the angel, Castiel presents the solution of going to Crowley for help to get him to do what he did with Samandriel to bring out Sam and get him to expel the angel. After finding "Sam", Castiel knocks him out and watches as Crowley tortures the angel to get information, admitting to Dean that its not easy for him to watch. He is also able to confirm that the angel did in fact heal most of the damage to Sam's body from the Trials. Castiel is furious to learn that the angel is actually Gadreel, the angel that allowed evil into the Garden of Eden and thus started all of the chaos on Earth. Dean eventually asks Castiel to possess Sam to help him force Gadreel out, but Castiel can't do that as he needs Sam's permission. However, Crowley can so at Dean's request, Castiel removes Sam's Devil's Trap Tattoo so Crowley can possess him. While waiting to see if it will work, Castiel reassures Dean. Finally, with Crowley's help, Sam expels Gadreel and Castiel heals the wounds he got from the torture, promising to finish Gadreel's healing of him though it will take time. When Dean leaves, Castiel stays with Sam.
In "First Born," Castiel stays with Sam in the bunker, trying to enjoy human things such as a sandwich but having a hard time as an angel. He also pushes him to make up with Dean. Castiel has nearly finished healing Sam and when he goes to give him his next treatment, he discovers that Sam still has some of Gadreel's grace inside him. Castiel discovers that they can use the residual grace to track Gadreel from the Men of Letters files and painfully starts extracting the grace from Sam. Castiel soon discovers that losing the grace is causing Sam to start to revert to the state he was in before Gadreel possessed him, but Sam insists they keep going as he wants to make up for his past which Castiel reluctantly agrees to. Eventually Sam's condition deteriorates badly and Castiel chooses to finish healing him completely, destroying the rest of the grace rather than sacrifice Sam even though they might not have enough grace for the spell. Castiel explains that being human has taught him that he was wrong in the past about doing whatever it takes to achieve what he wants and that he empathizes with Sam as he is the only one who has screwed up more times than Sam has. With this, Castiel officially loses any remaining disgust he holds towards Sam and his nature. After the spell fails, an appreciative Sam gives a stunned Castiel a hug and he returns it.
Following the defeat of Metatron, Castiel begins gathering rogue angels. Sam eventually calls to tell him that Dean is a demon, much to Castiel's discomfort. After Crowley provides Castiel with extra grace, Castiel rushes to the bunker to rescue Sam from a murderous Dean Winchester.
In Inside Man, Sam begins a plan to remove the Mark of Cain from Dean, he allows Castiel to help him. The two keep this mission a secret, and go as far as to recruit the help of Bobby Singer, Charlie, and Rowena. Castiel goes to Heaven to meet Bobby and retrieve Metatron, who is believed to know a cure for the Mark. Upon his return, Castiel delivers a letter from Bobby to Sam. When Rowena and Charlie are asked to help, Castiel is tasked with guarding the witch to ensure Charlie is comfortable.
Afterwards Sam is later happy to see Castiel regain his own grace and both agree on not telling Dean how they did it.
During Angel Heart, Castiel calls in the Winchesters for help with Claire Novak. Sam even defends Cass' possession of Claire's father, since that helped saved the world. Sam and Castiel are united in benching Dean from the case, due to his uncontrollable nature with the mark. During the case, Sam informs Castiel of the long thought extinct Grigori who kidnapped Claire's mother and kills her later. They work together in fighting him but watch Claire kill Tamiel instead.
They soon succeed in removing the Mark of Dean but at the cost of freeing The Darkness.
Some time after The Darkness was released, Sam is reunited with a sick Castiel and helps the angel search for his "crappy" car. When the spell cast upon Castiel takes over, Sam is the one to point a gun at Rowena's head to make her undo the spell. Afterwards, Sam joins Dean in insisting that Castiel rests, and in "Baby", Sam introduces Castiel to Netflix.
When Sam ends up trapped inside a cage with Lucifer in "The Devil in the Details", both Castiel and Dean rush to help him fend off the archangel. All three seemingly escape unchanged.
In "The Vessel," when Dean gets left behind on the USS Bluefin due to warding sigils, Sam works with "Castiel' to find a way to bring him back. Sam offers the use of his soul to power a spell that can remove the warding's on the submarine, but Sam soon discovers that "Castiel" is in fact Lucifer.
Lucifer takes Sam upon his offer and proceeds to penetrate his chest, causing Sam immense pain. Before Lucifer can do any serious damage, Castiel uses every ounce of his strength to regain control of his vessel and save Sam. Although Castiel is forced to surrender control back to Lucifer so the archangel can rescue Dean, Castiel was able to keep Sam out of harm's way.
However, the revelation that Castiel said "yes" convinces Sam that Castiel wants to be a vessel, and thus does not wish to be saved. Dean persistently argues that this is not the case, and Sam, hoping his own beliefs are untrue, has assisted in every attempt made to rescue Castiel.
Sam and Castiel are reunited after a botched fight against Amara ends with Lucifer expelled from his vessel in Alpha and Omega. When Dean prepares to confront Amara in their latest plan, Castiel promises Dean that he will watch out for Sam and make sure he doesn't do anything stupid. Sam and Castiel later gather at a bar with Crowley, Rowena and God.
When Dean's mission appears successful, Castiel follows Sam back to the bunker, but is suddenly banished by a blonde woman.
Castiel returns to the bunker only to find Dean and a resurrected Mary Winchester. The three decide to rescue Sam from the blonde woman. The confrontation leads to a success and Sam is brought back home in "Mamma Mia".
Knowing Lucifer is still on the loose, Castiel leaves the bunker alone to deal with the archangel, whose freedom he blames on himself. Sam and Dean do not get involved in Castiel's hunt until "Rock Never Dies", when the trio, plus Crowley, track down Lucifer to Los Angeles. The four manage to prevent Lucifer's plan to murder a dozen human who are attending a concert he hosted under the guise of his vessel, Vince Vincente.
Lucifer escapes capture, however, the four continue hunting down the archangel as he takes on various vessels, until he reaches President Jefferson Rooney. As soon as Castiel senses it, he quickly informs Sam and Dean that Lucifer has now conceived a child. The gang make a plan to confront Lucifer's mistress and convince her to abort the child. On their way, the US Secret Service block their path and nearly arrest Sam, Dean and Castiel until Arthur Ketch, an associate of Toni Bevell, arrives and knocks the agents out.
Ketch offers them a weapon to expel Lucifer from the President; with Rowena in tow, the gang are successful in freeing the President from possession. Castiel leaves the area with Lucifer's mistress Kelly, while Crowley takes Rowena away, leaving the brothers unintentionally at the mercy of the US Secret Service, who arrive and arrest Sam and Dean for trying to assassinate the President.
Castiel tries to convince Kelly himself to abort the child she is carrying. To his horror, Kelly accepts that Lucifer is the child's father but runs away instead of aborting it. Unable to find her, Castiel waits at the bunker for Sam and Dean's return, but to his misery, the brothers do not return. Castiel and Mary seek out help from Arthur and Arthur's associate, Mick Davies, and the men are able to locate Sam and Dean at a secret prison called Site 94. Once there, Castiel is happily reunited with the brothers, the friends share a hug when reunited.
However, their happiness is short-lived when Castiel and Mary learn that Sam and Dean had offered their lives up to Billie in exchange for escaping the prison. When Mary offers himself up instead of her sons, an unwilling Castiel refuses to let any of the Winchesters die, as a result he kills Billie and reprimands the brothers for even thinking that this world doesn't need them. He declares that he will not let them sacrifice themselves as they are important to him and he'll deal with the consequences of their acts.
The three are very surprised by Castiel's actions and care for them and go back home to the bunker.
When the Nephilim was about to be born, Castiel briefly betrayed the Winchesters after realizing the goodness of the unborn infant. Cass also declares that the Nephilim needs to be born with his power intact, much to Sam and Dean's confusion. Sam and his family track down Cass to help him fight against Lucifer who had come to collect his son, before he shows them Apocalypse World which had been been opened as a result of the Nephilim's birth. Once the Archangel is sent to the other realm, Castiel arrives to stab him as Sam tries to warn him to no avail. However, when he returns to the main reality, Sam is briefly relieved until Lucifer stabs and kills Castiel, with Sam left devastated at the corpse of his close friend's lifeless vessel.
During Patience, Sam shows that he doesn't put Castiel's death on Jack's hands. Though it is clear, he does miss his friend.
In The Big Empty, after awakening in The Empty, Castiel tells the Cosmic Entity that the Winchesters need him and demands for his release as he will fight it for all eternity if he has to until he is freed from the realm. At the end, Castiel is resurrected just as he demanded.
During Advanced Thanatology, Castiel calls Dean from a service phone, as a sleeping Sam wakes up questioning his brother who gives him a shocked reaction. The brothers drove to a small town where they find Castiel standing by a payphone and are shocked to see him alive again.
At the beginning of Tombstone, the brothers question how Castiel can be alive as he explains that he was resurrected by the Cosmic Entity. Sam asked if Castiel was sent to Heaven but he tells them that he was put in The Empty as he describes his horrible experience in the void of nothingness. Sam even deduced that Jack had a part in bringing Castiel back before he embraces Castiel after confirming that his friend has truly returned.
In Devil's Bargain, Cass returns to the brothers and delivers shocking news which was Lucifer's return, his and the latter's capture and that Michael intends to invade their world. Sam asked about his mother and Castiel can only reveal she's alive but knows very little of her wellbeing.
In Good Intentions, Dean and Castiel are told by Donatello to gather the hearts of ancient warriors while Sam is left at the bunker. When they return, Sam tells them Donatello lost his mind. Sam was later put off by Cass taking matters into his own hands as he painfully took the spell from the prophet.
During Scoobynatural, Castiel searched from the brothers who were sent to the Scooby-Doo Universe and he ended up being sent there as well before finding the brothers. Along with the Scooby Gang, they defeated a Ghost Kid and were sent back to their world.
In Bring 'em Back Alive, Castiel was shocked to hear from Sam that Dean traveled to Apocalypse world and found no comfort in him being with Arthur Ketch. The two tended to the battered Gabriel and were able to get him to talk before they dealt with the attack of Asmodeus and his forces. Castiel also saved Sam from being killed by a demon and the latter thanked him. When Asmodeus prepared to kill both of them, Gabriel regained his courage and incinerated the demon.
During Beat the Devil, they journey to Apocalypse World and travel through a tunnel filled with vampires. When Sam is taken, Castiel goes after him but is too late and he stops Dean from the sight of his devoured brother, knowing it would horrify him. He was later surprised to see Sam alive again and were surprised to discover it was due to Lucifer who arrives as well.
In Exodus, Sam and Castiel both sought to keep Jack away from Lucifer, to no avail. The two fought off many angels to save Alternate Charlie and Ketch. They also evacuated many of the resistance to Earth and were successful. Sam along with Dean also comforted Castiel after he expressed sadness at Gabriel's death.
In Let the Good Times Roll, Sam and Castiel went on werewolf case with Dean and Jack. Sam was amused about the prospect of him, Cass, Dean, and Jack being able to retire from hunting if their success keeps up. However, they became aware of Michael's arrival and Sam stopped Cass from attacking the Archangel. This was the least of their concern after they learn of Lucifer's return. When Michael broke in the bunker, Sam was worried after Castiel fought Michael and was promptly overpowered by him. When Lucifer empowered himself with Jack's grace, Castiel was worried especially when Sam and Jack had been taken by him as well.
Despite sharing a desire to defeat Lucifer and save Sam, Castiel wasn't keen on the idea of Dean letting Alternate Michael possess him, knowing that once Lucifer was dead, Michael would take full control of Dean and they would be dealing with the same threat posed by Lucifer only this time by Michael.
During Stranger in a Strange Land, Castiel apologizes to Sam for letting himself be captured but Sam relieves him of guilt as he may have done the same.
In The Scar, Sam and Cass have been reunited with Dean after he was released from Michael's influence. They work to find the cause of the scar on Dean's arm and Castiel nearly joined them on a case but had to work with another issue.
During Unhuman Nature, they are worried over an ailing Jack's condition.
In Byzantium, the two work together to resurrect Jack and are successful after bringing in Lily Sunder. Castiel also told Jack not to tell Sam or Dean of his deal with The Shadow since he didn't want them to worry.
As of The Spear, they are ready to face Michael and worked to gather the items needed to fight him. Both are horrified to witness Michael taking control of Dean again.
During Nihilism, the two work to capture Michael and return to the bunker (with help from Billie). They use the Mind-link device and enter Dean's subconscious. They jog Dean's memory and help him fight Michael when he is revealed to be powerless and stalling for his rescue. After being overpowered, they help Dean lock Michael away in his subconscious, allowing him control of his body and stopping the Archangel's threat from spreading.
During Prophet and Loss, Sam secretly told Cass about Dean's plan to lock himself in a Ma'lak Box, in spite of Dean telling him not to. They were both united in trying to persuade Dean into doing otherwise.
As of Lebanon, Sam along with Dean mentions Castiel to John Winchester after he was pulled out of the past and he was amazed they live with an angel. Later on, an alternate version of Castiel is created as a result of John Winchester being pulled out of the past. Along with Zachariah confront the Winchesters, the alternate Castiel is shown to be the loyal soldier of heaven and doesn't know Sam and Dean who he attacks. This results in him being banished by Sam. Once John is sent back and history is corrected, the real Castiel returns to the bunker where he meets the Winchesters and asks what occurred as Sam and Dean promised to explain.
In Ouroboros, when Castiel was stunned by a Gorgon, Sam was worried for him and attempted to attack the threat and watched as Jack used his powers to heal him. When Michael took control of Rowena, Sam and Cass were tortured by him after they tried to stop him but were saved by Jack facing Michael. The two witnessed Jack kill Michael and were amazed at his feat, as well as seeing that he regained his power.
In Lebanon, Sam meets an Alternate Castiel who was created by a timeline where John Winchester was brought to the future. This Castiel appeared on Earth with Alternate Zachariah, who was angry about the fact that somebody's been messing with time. Sam was shocked to see this Castiel, trying to get through to him. However, this Castiel has no recollection of Sam and attacks the Winchesters on Zachariah's orders. After killing Zachariah, Sam uses the sigil to send Cass off when Castiel overpowers Dean and beats him to a bloody pulp. After history is corrected by John's return to the past, this Castiel ceases to exist.