2x14 Born Under a Bad Sign
The teaser starts with Dean, speaking on the phone with Ellen. Sam has been gone for a week now. Suddenly, he gets a call from Sam. Dean hurries off to him, who is dazed, and covered in blood. Sam tells him the blood isn't his, and that he doesn't remember a thing.
Trying to recover what happened during the past week, they find themselves at a house. Inside, they find a dead body, (enter Steve Wandell), a hunter. They watch the security videos in silent horror, seeing Sam slit Wandell's throat.
Dean is thrown off by what has happened, and they worry that Sam might be turning evil. Back at the motel, Sam asks Dean to make good his promise to kill Sam should he turn evil. Dean cannot bring himself to kill his brother, saying, "I'd rather die." To which Sam says, "You'll live to regret it," before knocking his brother unconscious.
Dean finally comes to in the morning. He traces Sam to Duluth, Minnesota. Sam has found Jem waiting tables in a bar. She first greets him with delight, but Sam's friendly greeting turns dark and he knocks Jem out.
When she awakes, she is bound to the pillar. Sam taunts her about how her father died. She came home from school and her father tied her up and beat her. Then her real father came home - a shapeshifter had disguised itself as her father. The shapeshifter killed her father while Jem watched.
Dean bursts in, and Sam pleads again for him to kill him, or watch him kill Jem. Dean is unable to go through with it, turning away from Sam. Dean suddenly turns around, splashing the contents of his flask on Sam.
It is holy water and it sears Sam, who is in fact demon-Sam. Demon-Sam bursts out the window, and Dean gives chase. The chase finally ends on a dock, where demon-Sam shoots Dean who falls into the water. Thinking him dead, demon-Sam leaves.
Jem frantically tries Dean's cell, before finding him wounded but alive. She fixes him, taking the bullet out of his shoulder. Jem offers to help, but Dean forbids her to follow.
Demon-Sam is at the hunters door, and the hunter who opens the door turns out to be Bobby. They catch up, who has returned with beer. As demon-Sam drinks up, he suddenly bends over, smoke coming out of his mouth. Bobby has mixed the beer with holy water and tells him, "Don't try to con a con man."
Demon-Sam wakes to find himself in the center of the Key of Solomon. Dean is already there, and Bobby starts the exorcism. Unfortunately, it doesn't work, and Bobby finds a binding link on Sam's wrist, effectively locking the demon inside of Sam. Demon-Sam starts with some incantations of his own, cracking the ceiling, and breaking the Key of Solomon.
Once free, he flings Bobby and Dean away, and starts to pound Dean up, telling him, he is in fact demon-Meg, who has crawled out of hell, and bent on getting her revenge. Before (s)he can waste Dean with a final blow, Bobby grabs demon-Sam's arm and burns the mark on Sam's wrist, destroying the link. The demon exits Sam, and escapes by the fireplace.
Bobby gives the brothers charm amulets to prevent future possessions, and tells them to keep Steve Wadell's murder a secret, as his friends will come for his killer.
Sam and Dean hit the road again.
Quotes
Sam (to Jem): You didn't even know, did you? You couldn't even tell Daddy from a monster.
SuperPretendWiki entry
2x16 Detroit Rock City
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