After witnessing Gwen meeting Morgana in secret, Arthur is promised by Merlin that he will find a way to break Morgana’s twisted control of the young queen.
Using the aging spell, the warlock seeks the counsel of the Dochraid. But seeing through his disguise, the old witch refuses to talk, which forces Merlin to threaten her with his magical sword. The Dochraid then reveals that the spell can only be broken if Gwen immerses herself in the waters of a sacred cauldron. But she must do willingly or risk falling into the Abyss for all eternity.
Back at Camelot, Arthur changes the route of a levy collection that Morgana plans to intercept, but does not reveal why to his knights. Mordred suspects something is afoot.
Arthur and Merlin head to the sacred lake with a sleeping Gwen; and are later rescued by Mordred after falling down a ravine. Morgana then appears with a fire-breathing dragon. While Merlin battles the dragon, Mordred knocks Morgana out – with magic.
At the cauldron, Merlin disguises himself as an old sorceress and, as Arthur leads Gwen into the waters, he finally breaks Morgana’s dark magic. The episode ends with Mordred telling Merlin that he knows his secret…