It's been one year since Morgana's betrayal. On Samhain , Morgana sacrifices Morgause, with her approval, to summon the mighty Cailleach to tear open the veil between the worlds. Cailleach informs her that Emrys would be her doom. The next day, Arthur, Merlin and the knights investigate the mysterious slaughtering of a whole village, and they're attacked by hellish creatures who kill by touch. Gaius later identifies them as Dorocha. As refugees flow to Camelot, Gaius tells Arthur a blood sacrifice is needed to repair the veil, and Arthur decides to sacrifice himself. Agravaine is shown to be in league with Morgana. Gwen asks Lancelot to protect Arthur. En route to the island of the Blessed, they stay the night at a ruined castle where they're also attacked by Dorocha. Merlin throws himself at them to save Arthur.