"Brother's Keeper" is the twenty-third episode and season finale of the paranormal drama television series Supernaturals season 10, and the 218th overall. The episode was written by showrunner Jeremy Carver and directed by executive producer Phil Sgriccia. It was first broadcast on May 20, 2015, on The CW. In the episode, Dean kills a hunter and decides to summon Death to help him with the Mark of Cain as Sam tries to stop him. Meanwhile, Castiel and Crowley meet with Rowena in an attempt to destroy the Mark of Cain. The episode received acclaim from critics, who praised the resolution of the Mark of Cain and the cliffhanger ending. Plot Dean (Jensen Ackles) continues to hunt demons with a new partner, Rudy. Investigating the death of a girl in Superior, Nebraska, the Mark continues to corrupt him. Dean finds the vampire holding the girl's friend, he kills the creature and makes him kill Rudy. Meanwhile, Sam (Jared Padalecki) and Castiel (Misha Collins) make Rowena (Ruth Connell) cast a spell to destroy the Mark of Cain. She agrees if she gains her freedom and Nadya's Codex. She realizes the spell requires to sacrifice her greatest love. Castiel enters her mind to see her greatest love is Oskar: a boy she befriended 300 years ago and granted immortality. Dean has visions of people he has hurt or killed and destroys his entire hotel room to stop them. Sam tracks him and arrives at his hotel room, but Dean is gone. He finds a note and the keys to the Impala, writing "She's all yours." Castiel summons Crowley (Mark A. Sheppard) to help him with the ingredients, although Crowley is still angry after Sam tried to kill him. Crowley realizes the man he met at the diner in the previous episode is Oskar. Dean arrives at a bar where he summons Death (Julian Richings), asking the Pale Horseman to kill him as the Mark is affecting him severely, using a smorgasbord of junk food as enticement. Death refuses, stating that he can't kill Dean without the Mark being passed over to someone else. He tells him that before the time, there was a being called The Darkness. God and his archangels managed to lock it away in a prison with the Mark acting as a lock and God entrusted it on Lucifer. But the Mark corrupted Lucifer, which caused him to transfer it