Camelot is hosting its annual sword tournament and knights from throughout the realm have come to compete for its coveted title. Among those hoping to win the crown is Knight Valiant. Armed with a magical shield, Valiant will stop at nothing to win his prize. Merlin tries to expose Valiant as a cheat, but even those closest to him do not believe his claims.

Battling with his faith, friendships and destiny, Merlin attempts to stop Valiant's evil scheme before Arthur becomes the next knight to die by his shield.

The evil sorceress Nimueh (Michelle Ryan) is back to wreak havoc on Camelot. This time Merlin is her target, and she tricks the young warlock into drinking from a poisoned chalice, causing him to fall dangerously ill.

Arthur must venture to the caves deep beneath the forest of Balor to obtain the antidote, but he does not realise he is walking into a trap. Determined to thwart his quest, Nimueh does everything she can to stop him.

Can Arthur overcome these magical hurdles and make it back in time to save his friend?