Merlin meets a kindred spirit but his new friendship is threatened when a deadly magical beast attacks Camelot.

When the Great Dragon attacks Camelot, Merlin must go on an epic journey to find the one man who can defeat the monster.

Merlin has an unexpected meeting with the mysterious Taliesin (Karl Johnson). 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 her estranged brother, Elyan (Adetomiwa Edun) and Arthur. 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?

When an old flame of Gaius's arrives in Camelot, Merlin is pleased to see a different side to his curmudgeonly mentor. But after discovering she is under the influence of a Manticore, a creature from the Old Religion, Merlin has no choice but to tell his old friend of Alice's evil intentions. Blinded by love, the old physician refuses to believe Merlin's story and the two friends fall out. With the King in danger and all signs pointing to Alice and her evil pet, Merlin must somehow make Gaius come to his senses before it is too late.

Camelot's legendary tournament has only one rule: there are no rules. As the mythic city fills with terrifying warriors, they are joined by Gilli (Harry Melling) - who despite his small stature has victory in his sights... and he has a secret weapon to help him - magic. As Gilli begins to realise the full potential of his powers, Merlin finds himself torn. Not only is his new friend putting his own life in danger, but his actions threaten to rip apart the very fabric of Camelot itself. Can Merlin make Gilli see sense before it's too late?