When Merlin is wounded at Camlann instead of Arthur, the two journey to Avalon in a final attempt to save the sorcerer's life. They receive help from an unexpected source, leaving Merlin battling a strange condition. Morgana pairs with a new adversary, who strikes frighteningly close to home, and in the face of a rising dark army Merlin and Arthur must defend the future of Albion.

More than three years after Reid is abducted by Tobias Hankel, he disappears from his apartment. His kidnapper, a long-time fan of Raphael's violent videos, will prove to be far worse than his predecessor. The BAU races to recover their youngest before time runs out, but the damage done may be irreparable.