4x21 When the Levee Breaks
Dean and Bobby lock Sam in Bobby's Panic Room, in order to help him withdraw from the effects of the Demon Blood. Sam starts to hallucinate - first he imagines he is being tortured by Alastair. Next he is visited by his fourteen-year old self who accuses him of abandoning his hope of being normal, and brings up his guilt of Jess' death. When Sam yells that he’s not guilty of Jess’ death, he turns to find Chandler Mulvaney in the room, asking him if he is sure of that, if he needs absolution.
Meanwhile, Rufus Turner rings Bobby with news of more of The 66 Seals being broken. Rachel has arrived and asks Dean if they’re doing the right thing - she is concerned that the detox will kill Sam. Bobby echoes her question, for but different reasons - he is wondering whether they should let Sam go after Lilith to stop the Apocalypse.
Still in Bobby's Panic Room, Sam sees his mom, who says she understands what he is doing, and gives him support.
Dean calls on Castiel, who tells Dean that Sam could kill Lilith, but that consuming that much Demon Blood would make him inhuman. Castiel says Dean can be the one to stop the Apocalypse, rather than Sam, and asks if Dean will do it. Dean agrees and swears fealty and obedience to God and the angels.
Sam starts experiencing more extreme symptoms - he is being flung around the panic room, so Dean and Bobby handcuff him to the bed. After they leave, Sam imagines Dean is taunting him and calling him a monster. At the same time the real Dean tells Bobby he would rather see Sam die than turn into a monster.
That night Castiel comes and uses his powers to release Sam's bonds and open the door to the panic room. Sam slips out, but is confronted by Rachel, who doesn't have the heart to shoot Sam. Sam knocks her out, steals a car and escapes.
Anna visits Castiel, and confronts him over his actions, but he says he is acting on orders, and she is taken captive by other angels.
Sam meets up with Ruby, and drinks more of her blood. Ruby tells Sam there are only two or three seals left to be broken. She says only "Lucifer's first" can break the final seal - and that is Lilith. This renews Sam's desire to kill Lilith. She says she has a lead on a demon close to Lilith, who is nearby.
As they prepare to leave, Dean arrives and tries to kill Ruby, but Sam stops him. Sam and Dean start to argue over what they should do, and things get more heated and bitter until Dean calls Sam a monster, and Sam hits him. They fight until Sam knocks Dean down and nearly strangles him.
As he turns to leave, Dean admonishes him with the Sam words John Winchester used so many years ago - that if Sam leaves he should never come back.
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