Merlin narrowly escapes with his life when he is attacked by a mysterious and terrifying creature with the body of an eagle and the head of a lion. At the last moment, a young stranger appears and manages to fight the monster away. A grateful Merlin introduces himself to the wounded hero, who tells Merlin that his name is Lancelot before promptly passing out.
Merlin rushes Lancelot to Gaius. Meanwhile, a distraught Uther and Arthur visit a village which has been torn apart by the mysterious winged beast. It has left all livestock intact, preying only on humans.
When Lancelot comes around, he tells Merlin of his dream to protect the kingdom by becoming a Knight of Camelot. Merlin has to tell a devastated Lancelot that only those of noble birth may serve. Such is Lancelot's upset that Merlin fakes some credentials for him. Though Lancelot is reluctant, Merlin persuades him to use them to convince Arthur of his nobility. Lancelot impresses Arthur with his fighting ability and quickly progresses through basic training.
When a sea of injured villagers arrives at Camelot, the King's concern about the mystery beast increases. Uther tells Arthur to prepare his men for battle. Aware of Lancelot's potential, Arthur moves his test forward so that he is able to fight alongside him when the beast strikes. Lancelot passes the test with flying colours and Uther makes him a Knight.
However, Lancelot and Merlin's merriment is short-lived. The following morning, guards storm Gaius' chambers and arrest Lancelot. Uther has found out about Lancelot's lies; he removes his knighthood and throws him in jail. Arthur tries to reason with Uther, but the King stands firm, he cannot have a Knight protecting him that he can't trust.
The Griffin strikes Camelot. Arthur and his Knights are ready, but have underestimated their opponent. Their weapons are useless and the beast is fast and strong. They manage to chase it off, but for how long?
Gaius discovers the identity of the winged beast. It is a Griffin, a monster that until now has been known only in legend. It is a creature of magic, and as such can only be defeated with magic. Gaius tells Uther of his findings, but his advice falls on deaf ears; the King is determined the creature is flesh and blood just like any other. Gaius is deeply concerned for Arthur's safety, and tells Merlin that he must harness the powerful magic needed to defeat such a beast, or Arthur will surely die.
Arthur visits Lancelot in jail. Lancelot is the best Knight he has ever fought alongside, and that is why he is letting him go. Lancelot is delighted, but Arthur knocks him down - Lancelot must leave Camelot and never return, or they will both have to face Uther's wrath.
As Merlin desperately tries to harness the magic he must master, Gwen comes running in - Lancelot has been freed and plans to go after the Griffin himself. A worried Merlin races from his chambers to help his friend.
Despite Lancelot's reluctance, Merlin insists on accompanying him on his crusade. The pair ride into the woods in search of Arthur and the other Knights. They find a bloody mess; the Griffin has attacked and taken no prisoners. As the Griffin strikes once more, Lancelot gallops towards the beast with his lance held high, while Merlin tries his hardest to enchant the weapon. It works. With a flash of blue light, the lance strikes the Griffin, killing it instantly. Arthur and the few remaining Knights crawl to their feet; they see that Lancelot has slain the monster. Arthur didn't see the magic and congratulates Lancelot on killing the griffin.
Back in Camelot, Arthur tells Uther that he must reinstate Lancelot's knighthood. Waiting anxiously for news, Lancelot tells Merlin he saw the magic used to kill the griffin. He promises to keep his secret, but he cannot take credit for killing the monster when Merlin was the real hero. Lancelot interrupts Uther and Arthur to tell them that he is leaving Camelot, but hopes to return one day having proved himself worthy of his title as a Knight of Camelot.
Merlin has pushed the limits of his strength to save Arthur, but even he may not be powerful enough to rescue Camelot€™s king.
In the battle foretold by the prophecies, all give their best, and Merlin wins the day.
Morgana may have one last trick up her sleeve to win the war.