Arthur’s coming-of-age celebrations are interrupted by a mysterious Black Knight, who comes crashing into the ceremony to challenge the knights of Camelot to a single combat. Young eager knight Sir Owain takes up the challenge to fight the next day, and as the Black Knight leaves, a shaken King Uther stares at the distinctive crest on his helmet.

The next day, a crowd gathers as Sir Owain and the Black Knight prepare to do battle. It looks like Sir Owain doesn’t stand a chance against the fearsome warrior but Merlin is delighted when Sir Owain strikes his opponent. But the Black Knight seems to unaffected by the blow, and goes on to kill Sir Owain.

Later, Gaius takes Merlin to see the tomb of Tristan De Bois and is horrified to find it’s empty – his body is gone. Gaius explains that the Black Knight’s helmet bears the crest of Tristan De Bois, the brother of King Uther’s wife, who blamed Uther for his sister’s death in childbirth. Gaius is sure the Black Knight is Tristan De Bois, brought back from the dead to exact his revenge.

Merlin discovers that the only way to kill a vengeance wraith is with a sword forged in a dragon’s breath – but time is against him as Arthur, determined not to lose any more knights, is due to fight the Black Knight the following day…