When Merlin has an unexpected meeting with the mysterious Taliesin, the wizened old sorcerer takes the young warlock to the crystal cave and shows him a glimpse of the future. But this gift turns out to be more of a curse when, to his horror, Merlin sees Morgana, set to kill Uther.

Merlin knows he must do all that he can to stop the future from playing out. But changing the pages of destiny is a dangerous game, and his actions have fatal consequences. With the whole of Camelot in a state of grief, can the young warlock undo the damage he has caused, or is it too late?

Gwen finds herself with an impossible dilemma when she is forced to choose between Arthur and her estranged brother, Elyan. With one of them certain to die at Cenred's hand, who will Gwen choose? The love of her life, or her only sibling?

Loyalties are tested to the limit and friendships are thrown to the fore as Arthur, Merlin and Gwen work together to try and find a way out of the situation. But with Morgana and Morgause doing all that they can to scupper the threesome's plan, can good conquer evil, or will Gwen lose another of those she loves?