While picking mushrooms in a forest, Merlin is attacked by an enormous winged beast with the head of an eagle and the body of a lion. The creature corners him but is chased away by a young man with a sword. Merlin's rescuer introduces himself as Lancelot. Later, King Uther and Prince Arthur search the forest for signs of the creature. It has taken human victims from the nearby village but attacked no livestock: the creature has developed a taste for human flesh. Uther orders Arthur to prepare Camelot in case the creature should head for it.
Lancelot has been brought to Gaius and treated for superficial wounds. He makes a full recovery and later tells Merlin about his ambition to become one of the Knights of Camelot. Merlin promises to put in a word for him with Arthur. Unfortunately, Arthur states that only those of noble blood are eligible for knighthood. Lancelot is devastated. He is the only survivor of a village which was massacred by raiders, and has been training in combat ever since in order to achieve his dream of defending Camelot.
Merlin uses his magical powers to create a forged seal of nobility for Lancelot to use. Lancelot is reluctant to lie but Merlin convinces him that all he needs is a chance to prove his worth. Gwen (Guinevere) fits Lancelot for his chain mail and they seem to be very taken with each other. Gaius chastises Merlin for forging the seal of nobility, but Merlin passionately declares that the rules of knighthood are unfair and this is the only way he can repay Lancelot.
At the same time, survivors from another village attacked by the monster arrive at Camelot. Uther deduces that the mysterious creature is moving towards Camelot. He tells Arthur to prepare the royal knights to fight. Because of this, Lancelot's test of knighthood is brought forward. He must last one minute in a duel with Prince Arthur. Lancelot feigns defeat and then attacks when Arthur is not looking. This is successful and he is appointed Sir Lancelot. However, Uther is suspicious and orders the seal of nobility to be examined by the court genealogist, Geoffrey of Monmouth.
At the celebrations for Lancelot's knighthood, Merlin jokingly asks Gwen who she would fall in love with if she had the choice between Arthur and Lancelot. Gwen says she will never have to make that decision. Lancelot is arrested the following morning when it is discovered that he's not a real nobleman. He is thrown into the dungeons. Arthur says Lancelot still proved himself capable to fight, but the king insists that Lancelot has betrayed their trust and is not worthy of the honour.
Gaius has discovered that the monster terrorising the villages is a Griffin, a creature previously thought to be only mythical. The Griffin arrives in Camelot and battles with Arthur and the royal knights. It destroys Arthur's weapons and later disappears. Gaius says that the creature is magical and can only be defeated by magic, but Uther insists they lure the Griffin and kill it that evening. Gaius tells Merlin that he must use magic to defeat the Griffin or Arthur will be killed.
Arthur comes to release Lancelot from prison. He is regretful that Lancelot cannot serve as a knight, but orders him to leave Camelot before the king finds out. Lancelot asks Gwen to provide him with weapons and armour so that he can fight the Griffin anyway. She begs him not to go. Merlin discovers that Lancelot plans to battle the Griffin, and rushes off to join him. Meanwhile, the royal knights have arrived at the Griffin's lair; however, the monster slaughters the knights and badly wounds Arthur. Lancelot arrives as the beast is about to finish him off, and charges at it. Merlin uses a very powerful spell which he had practiced with Gaius but been unable to use. Lancelot's spear becomes magically charged and he kills the Griffin.
Uther is furious that Arthur defied him and released Lancelot. Arthur protests that Lancelot has saved his life and fought with honour. Lancelot knows that Merlin used magic to defeat the Griffin and promises to keep Merlin's "secret" safe. Uther and Arthur argue over whether or not to restore Lancelot's knighthood, but Lancelot cannot stand to lie any more. He asks for their forgiveness and leaves Camelot. Gwen sadly watches him go, but Merlin foresees Lancelot will return to them one day.