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?