Gwen is mistaken for Morgana and kidnapped by the savage outlaw Hengist. Uther refuses to pay her ransom, so Arthur defies his father and heads out into dangerous enemy territory to fight for Gwen's freedom.

Merlin suspects Arthur's devotion to Gwen is more than that of a prince to one of his subjects. How will Arthur react when he discovers Gwen is not alone in Hengist's castle? She and Lancelot have found each other again, and powerful feelings are rekindled.

Newly crowned Queen Catrina settles in as Camelot's first lady. As her true troll nature surfaces, her influence over Uther increases, and the repercussions are felt throughout the kingdom.

When Catrina accuses Merlin of stealing, he is forced into hiding. Forced to sneak around the castle, Merlin must find a way to expose Catrina's true form without getting caught and beheaded. Even if he succeeds, is it enough to break her powerful magic? Or will Camelot be stuck with a troll queen forever?