The Werther Project
Sam learns that former Men of Letters, Magnus, once built a magical box and Sam sets out to find it in the hopes it can cure Dean of the Mark of Cain. However, what he’s not prepared for is the deadly alarm system Magnus set up on the box. When Sam opens the box, he puts both his and Dean’s life in danger.
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More from this season
S10 E1
Black
Dean is a demon and running amuck with Crowley while Sam tries to figure out what happened to his brother. Meanwhile, Castiel is dealing with his fading grace.
S10 E2
Reichenbach
Crowley is worried that Dean, driven by the mark, is getting out of control. Sam struggles to escape from Cole. Hannah tries to convince Metatron to give Castiel his grace back.
S10 E3
Soul Survivor
Sam continues to try to save Dean from the Mark of Cain. Realizing that Dean's antics are causing problems for him in hell, Crowley seeks help from a reluctant Castiel.
S10 E4
Paper Moon
Sam and Dean investigate a series of werewolf attacks.