Travis called Sam and Dean to help him because he was injured and needed help to find Jack. Travis killed Jack's father in 1978, not knowing that his wife was pregnant at the time, and she subsequently gave the baby up for adoption. He believed that Jack had the rugaru gene within him, but wanted to make sure that he had begun to exhibit signs of his oncoming change. The Winchesters observed that Jack had developed a taste for raw beef. Travis told them that was just how the transformation began; Jack would eventually graduate to indulging in "long pig"—another term for human flesh.
When Jack's wife Michelle cut her finger, he was momentarily transfixed on her bleeding wound. He was confused, and overcame this by abruptly leaving the house without assisting her. He headed to a bar and instigated a fight with, and broke the hand of, a drunk patron who was harassing a female bargoer. He returned home to his angry wife, genuinely apologetic for leaving her to drive herself to the emergency room. She forgave him, but soon became angry again when he suddenly became very sexually aggressive with her. Some time later, Sam and Dean arrived in Jack's backyard as he inattentively watered his lawn in order to talk to him about his seemingly imminent transformation. They informed him that his real father was a rugaru.Jack regarded all this with outward disbelief and some degree of insult, but also with a look that indicated his hidden recognition of the matter. They shared with him their (mostly Sam's) belief that he could defeat his hunger, and thus hold back the change. If not, they would have to "stop him". Jack reacted with anger, asking aggressively if someone had "stopped" his biological father. They affirmed, and he demanded that they get off his property while threatening them with the cops.
Later on, Jack almost gave in to the rugaru within him, but catching his reflection in his would-be victim's window reinforced his human side, and his desire to stay that way. He headed back home, only to be knocked unconscious by Travis as he arrived. He woke up bound to a chair, believing Travis to be a burglar until he revealed why he was really there. Jack pleaded with him, telling him that Sam and Dean told him that his fate was not necessarily sealed. When he resolved that Travis was going to kill him, he begged him to let his wife go.
Travis, who was honestly distraught about the situation, told Michelle to repeat what she had already told Travis: she was pregnant. Travis, though regretful, had decided that he could not allow another rugaru spawn to exist because he wouldn't be around long enough to monitor its maturation. Watching Travis prepare to burn his house down with his wife in it caused an emotional rush in Jack, which helped him to break free, overtake Travis, and take his first bite of human flesh. Soon after, he devoured Travis, as his wife watched in horror. Jack took on a pale, black-eyed, monstrous appearance as he slowly approached his wife and untied her bonds. She screamed at him to stay away from her, ran out to her car and sped away. Later, Sam and Dean arrived on scene, only to be knocked out by Jack. Sam woke up in a locked closet and tried to reason with Jack one last time, realizing that Dean was unconscious. Jack snapped at him, blaming the hunters for what happened to him; how he could ever see his family again as what he had become? Sam told him that it wasn't what he was that mattered, only what he decided to do about it.
Sam finally worked his way out of the closet and found Jack crouched over Dean, who was still unconscious and bleeding. Jack turned and made eye contact with Sam, and then charged him. Sam set him alight with a flamethrower and watched him drop to the floor. Dean finally came to, and they shared regretful looks.