S10, E10: After the massacre at the ranch, Dean, Sam and Castiel double their efforts to find a cure for the Mark of Cain but there is nothing in the lore that can help them. Desperate, Castiel comes up with an idea that Sam deems the “single worst idea I’ve ever heard.” Meanwhile, Rowena continues to plot against Crowley, and Castiel tries to mend his relationship with Claire who is plotting revenge against Dean for killing her friend.