Merlin (2008) (2008)

S4E1 The Darkest Hour (1)

The wicked sorceress Morgana calls upon the powerful gatekeeper, the Cailleach, who unseals a portal to a nightmarish realm, unleashing terrifying creatures into their world. As Arthur and his devoted knights prepare for battle, Merlin uncovers a chilling truth: the only way to halt the chaos is through an unfathomable sacrifice.