The Darkest Hour (1) Merlin : Season 4 Episode 1
TV-PG BBC One 45m
Aired: October 1st, 2011 @ 7:45 PM EST on BBC One
Evil sorceress Morgana summons mighty gatekeeper the Cailleach, who opens a door to another world from which hellish creatures pour forth. As Arthur and his loyal knights take up arms, Merlin discovers the only thing that will stop them is an unimaginable sacrifice.
