On the night of November 2, 1983, the demon Azazel entered the nursery of baby Sam Winchester and infected him with demon blood. As Mary Winchester interrupted him, Azazel murdered her by pinning her to the celling and then setting her and the Winchester house on fire. As a result, her husband John became a hunter dedicated to hunting down Azazel and killing him to avenge his wife's death and dragged his sons Sam and Dean into the life with him. At some point John determined that Azazel was a demon and was determined to find a way to kill a demon despite it being thought impossible. He heard of the legend of the Colt, a gun that was said to be capable of killing anything, but could never find it or proof that it was more than a legend.
At some point in the past before 1973, hunter Daniel Elkins somehow got his hands on the Colt, possibly having it passed down from an ancestor who may have retrieved it in 1861 after a future version of Dean used it to kill a phoenix. Elkins specialized in hunting vampires and at some point in the past, killed the family of the vampire Luther, though Luther himself survived. In 2006, several members of Luther's nest, led by his mate Kate entered a bar where Elkins was drinking in Manning, Colorado. Recognizing Kate and thus knowing the group are vampires, Elkins fled to his home where he loaded the Colt to use against the vampires. However, they got inside and killed Elkins before he could use the Colt on any of them. The group then took the Colt with them.
While looking for a case, Sam finds an article on the murder of Elkins which states that the police thought it was a bear attack since he was mauled, but there were signs of robbery, indicating it was something else. Dean recognizes the name and looks in his father's journal and finds Elkins name and phone number. Sam and Dean decide that since Elkins' name was in the journal, his death is worth checking out.
Arriving at Elkins' cabin, the Winchesters break in and find salt and a hunting journal that dates back to the 1960s, causing them to realize that Elkins was a hunter. Searching the cabin, they realize that whatever killed Elkins, there was more than one of them and Dean finds scratches in the ground spelling out the location and combination of a post office box and realize its a mail drop similar to what their father would do. Checking the post office box, they find a letter addressed to J.W. which they realize is likely their father. As they discuss what to do with the letter, John himself shows up, having come to investigate Elkins' death himself and having not approached them until he was sure they weren't followed. John explains that Elkins taught him a lot about hunting, but they had a falling out so he never mentioned Elkins to his sons. John reads the letter and is shocked to learn that Elkins had the Colt the whole time and asks if Sam and Dean saw an old Colt revolver when they searched Elkins' cabin. When Dean tells him there was an old gun case but no gun, John realizes that Elkins' killers took the gun and tells his sons they need to get after it. Sam is shocked that John wants them to join him, but John just tells him that if Elkins is telling the truth about having had the gun, they need to get it but refuses to elaborate beyond the fact that the gun is important. When Sam points out that they don't know what killed Elkins, John informs his sons that it was what Elkins hunted best: vampires. Sam and Dean are shocked as they didn't think vampires were real and John never even mentioned them before. John tells them that he'd thought that vampires were extinct, wiped out by Elkins and others like him, but he was wrong. John then fills them in on the differences between real vampires and fictional vampires.
That night, the vampires ambush a young couple by having Beau lie in the road so they stop to check on him. Once they do, the vampires ambush and capture the couple and take them to their nest. At the nest, Luther has the other vampires drain the man while Kate informs him of Elkins' death. Luther isn't happy as he knows other hunters will recognize what killed Elkins and come after them as a result. When Kate insists she did it for Luther's family, he tells her that revenge means nothing if your dead. When Luther spots the Colt, he's shocked as he recognizes the gun and tells Kate that he knows it and its no ordinary gun. Later, spotting the captured woman watching them, Luther and Kate decide to turn her into a vampire as well. Luther cuts Kate's arm and she then sucks blood from the wound before kissing the woman, forcing blood into her mouth and turning her to Luther's delight.
Listening to a police radio, John hears a report about the missing couple who had called 911 before Beau attacked them. Once the cops got to the scene, they only found the couple's abandoned car and no sign of Beau or the couple. John realizes that the vampires have abducted the couple and awakens his sons to go after them. Checking with the cops, John is able to confirm its the vampires as he finds a vampire fang and informs Sam and Dean of this along with the fact that the vampires seem to be moving west. As the Winchesters chase after the vampires, Dean reads Elkins' journal to learn more about them and finds out that vampires nest in groups of eight to ten, smaller packs are sent out to hunt for food and the victims are taken back to the nest to be fed on for days or weeks, making Dean wonder if that's what happened to the couple that was kidnapped. However, Sam is angry with John not telling them more than what they need to know and just barking orders at them and expecting them to follow. John eventually lets them know to take the next exit as he believes they've got the vampires' trail, but when John won't tell them how he found the trail, Sam ends up having had enough and forces John to stop his truck and talk to them. Sam demands answers from John about why, after telling them its too dangerous for them to be together, he's suddenly taking them after the Colt and demands to know what's so important about it. John refuses to tell him and Dean eventually gets Sam to back off, though not before he mutters about this being why he left in the first place, starting another argument about Sam leaving. Dean eventually manages to break it up, but it leaves both John and Sam furious with each other.
The next morning, the Winchesters observe as Luther greets a returning Beau and Dean is surprised to learn that sunlight really doesn't scare them. John explains that while sunlight hurts them, only decapitation will kill them and while vampires sleep during the day, they still need to be careful as the vampires can still wake up. John tells them that the plan is to walk right in and the three arm themselves with machetes. As they arm themselves, John decides to tell them what's so important about the Colt. He explains the legend of the Colt, finishing by telling his sons that the legend states that the gun can kill anything. Sam realizes why John wants the gun: if it can kill demons, he can use it to kill Azazel and get his revenge for his wife's murder. John confirms this, telling his sons that ever since he picked up Azazel's trail, he's been looking for a way to kill him and if they can get the Colt, they may have that way.
The Winchesters make their way into the barn with John going into Luther and Kate's room where the Colt is and Sam and Dean looking for the vampires' victims. Sam and Dean find the kidnapped woman still tied to a pole and the vampires' other victims locked in a cage and set about freeing them. However, the woman wakes up, now a vampire herself and roars to alert the other vampires to the hunters presence in their nest. Sam and Dean quickly flee the barn, chased by the other vampires, but get away. The noise alerts Luther and Kate too, but John escapes by breaking a nearby window, causing the two vampires to cower from the light for a moment. Reaching his sons, John tells them that the vampires won't chase them until its night and that once a vampire has your scent, its for life. John then sends Dean to find the nearest funeral home in order to get them dead man's blood to use against the vampires.
Dean gets the dead man's blood for the Winchesters and while they wait for him, Sam and John make some amends from their issues with each other over Sam leaving for Stanford. After getting the dead man's blood, they set up a trap for the vampires where Dean pretends to have car trouble while Sam and John wait in the woods to ambush them. Sure enough, Kate shows up with another vampire named Hank, pretending to be there to help Dean. However, Dean tells her he won't go home with her as he draws the line at necrophilia and Kate attacks him. Though she tells him she could have fun with him, Dean tells her he doesn't usually stay with someone for long and certainly not eternity. While Kate and Hank are distracted with Dean, John and Sam shoot the two vampires with crossbow arrows soaked in dead man's blood, causing Kate to drop Dean. Kate is just annoyed at being shot until John tells her that the arrows are soaked with dead man's blood which is a poison to vampires. Kate passes out and not needing Hank, John decapitates him, killing him while Sam and Dean take Kate prisoner.
To keep the vampires from finding them until they're ready, John has them burn saffron, skunk's cabbage and trillium and spread the ashes on their clothes as it will disguise their scent for a while. John plans to have his sons raid the nest while he trades Kate for the Colt since vampires mate for life and Kate means more to Luther than the gun. John tells them that the blood sickness from the dead man's blood will wear off soon and they won't have long, but Sam thinks they need only half an hour. John tells them that once they've raided the nest, they are to leave the area immediately. When Dean points out he can't take on all of the vampires by himself, John tells them that he'll have Kate and the Colt and will be alright. Sam realizes that John intends to go after Azazel alone once he has the Colt and John confirms that, telling them that they're his children and he wants to keep them safe. Dean tells John he can't be too worried about that as he knows what they've been hunting and has even sent them on a few hunting trips himself and John tells them that Azazel is very dangerous and he can't make the same moves against him with Sam and Dean there that he could without them as he would be worried about keeping them alive if they were with him. John doesn't expect to make it out of the fight alive and he can't watch his children die as well as his wife. Dean insists that they are stronger as a family and John knows it so they should go after Azazel together, but John just orders them to raid the nest and get out of the area before leaving, ending the discussion.
Beau returns to the nest and informs Luther that Hank's dead and Kate's missing. As the vampires discuss Kate's fate, John drives by in his truck and Luther senses Kate in the truck. Luther takes all but Beau with him after John and Kate and while the other vampires are gone, Sam and Dean sneak into the nest. Dean kills Beau and he and Sam release all of the vampires victims before disobeying John's orders and going to help him.
John drives down the road with Kate and Luther and the other three remaining vampires chase him down in two cars, eventually getting in front of his truck and forcing John to stop. John informs Luther that Sam and Dean are cleaning out his nest and brings out Kate upon Luther's demand. Kate tells an angry Luther about John dosing her with dead man's blood and John demands Luther trade the Colt for Kate. When Luther tells John he can't kill all of the vampires with it before they kill him, John tells him he's saving it for something else and demands the gun or he kills Kate. Luther lays the Colt in the middle of the road, but when John grabs it, a recovered Kate manages to break free of the ropes he's tied her up with and knocks against his truck, causing him to drop the Colt. Luther attacks John as well, knocking him out.
Before Luther can kill John, Dean takes down one of the other vampires with a crossbow arrow soaked in dead man's blood. Sam engages Luther while Dean takes out one of the other vampires with another arrow. However, Sam is defeated and when Dean grabs a machete to help him, Luther takes Sam hostage and threatens to break Sam's neck to force Dean to disarm himself. Luther demands to know why hunters can't leave vampires alone as they have as much right to live as humans do and is surprised by a recovered John telling him "I don't think so." Luther turns to find that John has recovered the Colt and is aiming it at him. Before Luther can react, John shoots Luther in the head with the Colt, killing him and saving Sam.
An enraged Kate tries to charge the hunters to get revenge, but recognizing that they are outmatched, the young woman Kate had turned, the only other vampire left, gets Kate to flee with her in one of the vampires' cars. With Luther dead and the still-standing vampires gone, the Winchesters presumably kill the remaining two vampires Dean had taken out before leaving the scene.
As his sons are packing to leave, John confronts them on disobeying his orders and coming back for him. When Dean points out that they saved his life by doing so, John agrees to their surprise. John tells them that as much as it scares him to lose them, the battle with the vampires proves that they are stronger as a family and asks his sons to come after Azazel with him which they both eagerly agree to.
Shortly after the battle, the demons get word of the Winchesters getting their hands on the Colt and take it as an act of war. To force them to turn over the Colt, the demon Meg starts killing hunter friends of theirs such as Pastor Jim and Caleb.
- First encounter with vampires which would become one of the most recurring monsters on the show despite the fact that its indicated that they are nearly extinct at the time of the battle.
- Introduction of the Colt which is an important plot device in the remainder of the first season, the second season, the third season and the first half of the fifth season.
- While Sam and Dean use crossbows with dead man's blood-tipped arrows against the vampires during this battle, they never use crossbows again though they continue to use dead man's blood against other vampires they encounter.
- Dean later meets Daniel Elkins while time traveling to 1973 where he borrows the Colt from a younger Elkins. He also meets a potential ancestor that Elkins possibly got the Colt from while traveling back to 1861 where the Winchesters borrow the Colt from Samuel Colt himself.
- Only battle where John is actually shown to kill a monster on-screen, in this case Hank and Luther. He is mentioned to have killed many more monsters over his career, but aside from driving off a Shtriga, his encounter with Meg and Tom and helping his sons in the final battle with Azazel, John is not seen in action over the course of the series. Here, he is shown to be a knowledgeable and experienced hunter though Sam feels that Dean surpasses him and everyone else they know by Trial and Error.
- John is able to somehow figure out where the vampires have their nest which he doesn't explain to Sam and Dean. Besides knowing they are heading west from the crime scene where the vampires abducted the young couple and then suddenly figuring out where the vampires are hours later, there's no indication as to how he does this. However, John may have simply looked up abandoned or empty buildings in the area and found the barn as a possibility as Sam and Dean generally find nests in that way once they know where to look as shown most prominently in Alex Annie Alexis Ann.
- In the final battle with Azazel, there is a similar situation to John recovering the Colt while Luther is distracted by Dean and then killing him. In that case, the ghost of John himself distracts Azazel which allows Dean to retrieve the Colt and finally kill him.