A mysterious, scarred man enchants a bunch of flowers, which are then delivered anonymously to the Lady Morgana. As she sleeps, an enchanted beetle creeps from the bouquet and enters her ear.
Soon, Morgana is desperately ill, unresponsive and pale. Gaius is summoned to help, but cannot find the cause of the disease. An anxious Uther puts the pressure on Gaius to cure Morgana before it's too late, but he is unable to find an effective treatment. The scarred man, Edwin, arrives at the palace - he is a physician and claims to have a cure for all ills. Desperate for answers, Uther urges him to start examining Morgana right away.
Edwin secretly uses magic to remove the beetle from Morgana's head, thus curing her and undermining Gaius. Though grateful for his help, Gaius is suspicious of the mysterious stranger and his methods. Uther, meanwhile, is impressed and encourages Edwin to stay in Camelot.
Merlin is curious about Edwin and takes it upon himself to see what he can find about this mysterious stranger. Snooping around the physician's chambers, he finds a wooden box of 'dead' beetles. Reading the spell on the lid, Merlin accidentally conjures the beetles to life. Edwin catches Merlin and realises he must have magic to be able to perform such a feat.
Meanwhile, Gaius starts his own investigation. He enlists the help of his old friend Geoffrey of Monmouth and manages to get his hands on a copy of an old records book from the time of the Great Purge. Studying the book from dusk till dawn, Gaius finds what he was looking for - evidence of Edwin's true identity.
Gaius confronts Edwin with his findings: Edwin's parents were sorcerers when Uther banned magic. Edwin received his scars trying to rescue them from the flames that killed them...he is in Camelot to exact his revenge on Uther. Gaius threatens to go to the King, but Edwin is one step ahead of him and demands he keep quiet or he will reveal Merlin is a sorcerer and condemn him to death at Uther's hand.
With Gaius' hands tied, Edwin inveigles his way further into Uther's court and Gaius is sacked as court physician. Deeply concerned for the King's safety, Gaius visits the Great Dragon looking for advice. Much to his surprise, the Great Dragon tells Gaius that Merlin's life is more important than the King's and if Uther should have to be sacrificed in order to save the future warlock then so be it. Gaius decides there is only one thing he can do. He leaves Camelot, and Merlin is devastated.
With Edwin's path now totally clear, he puts the final pieces of his plan into place, drugging the King and then releasing one of his magical beetles into his chambers.
Just when it looks like all is lost, Gaius returns to Camelot and confronts Edwin. Gaius is forced to use magic, but he is weak and Edwin soon overpowers him. He is only saved when Merlin arrives in the nick of time - and kills Edwin himself.
However, they may be too late - Uther is already ill. Merlin has to use magic to remove the enchanted scarab from his ear. He allows Gaius to take the credit. Uther reinstates his old physician and tells Gaius that he will never doubt him again.
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.