The devious Knight Valiant rides into Camelot to compete in the annual sword-fighting tournament, bearing an enchanted shield from which he can command deadly snakes. As Arthur prepares for the fight, a disgruntled Merlin discovers Valiant’s magical secret and realises that the prince is in mortal danger.

Merlin presents his evidence to Arthur, who hasn’t exactly been impressed with his servant’s lack of talent for his new job. Arthur is initially dubious, but takes a leap of faith and decides to trust the youthful Merlin. Arthur makes his case to his father King Uther before the entire royal court, but is forced to withdraw the allegations.

With his father disappointed in him, Arthur blames Merlin for his humiliation and dismisses him. Realising he must master the magic that brings the snakes to life in order to expose Valiant and save Arthur, Merlin struggles through the night to learn the incantation. But by the day of the tournament final, Merlin is running out of time.

As Arthur fights Valiant, dodging snake bites from the magic shield, Merlin finally masters the magic. He races to the amphitheatre and uses his own powers to expose Valiant by revealing the snakes to the world. But is Merlin too late to save Arthur – and will his own magic abilities be revealed?