Merlin is about to tuck into a giant ham, when he and Gaius are summoned before the King. There have been reports of miraculous medical recoveries throughout the kingdom and he thinks it may be witchcraft. Gaius is ever cautious and suggests that he will have to investigate.
Merlin and Gaius go to the tavern to question the innkeeper, who tells them that his wife went to see a woman in the Lower Town, who gave them a cure. When Gaius examines the cure, a tiny fountain of magical sparkles rain down on his hand. Gaius tells the King that there were no magical goings on. Merlin can't believe Gaius got away with such an audacious lie.
Late at night, Merlin sees Gaius leaving their chambers. Merlin follows, carefully keeping himself out of sight. Gaius knocks on the door of a hovel, and Alice answers. A patrol of guards approach, and Merlin is forced to flee.
Gaius and Alice get reacquainted. It has been 20 years since they were together, but Gaius still recognised her magical healing arts. But when he leaves, an evil Manticore appears from its hiding place. Alice tries to protest about deceiving Gaius, but her eyes film over black - she is possessed.
Merlin questions Gaius as to his whereabouts. At first, Gaius is angry that Merlin followed him, but the old physician quickly softens. He tells Merlin that he and Alice were once engaged to be married, but when Uther declared war on magic, she was forced to flee. Merlin is happy for Gaius that his old love has returned.
At night, Merlin hears voices and moves to investigate. He peers through a crack in the door and sees Alice talking with the Manticore. She extracts some black liquid from its tail and places it in a vial. Disturbed, Merlin probes Gaius on Alice's history; he admits that she used to practise dark magic. Merlin wants to prove that she still is, but his investigation of her things proves fruitless and only serves to anger Gaius.
Later, the warning bell sounds out across the palace. Merlin and Gaius rush to the King, but Alice already knows the cause for concern - it is the poisoned medicine she prepared. Arthur is frantic, and Gaius gets to work diagnosing. He sees the King's eyes are completely black, and puts Uther's medicine in his pocket.
When Merlin gets Gaius alone, he tells his mentor that Uther was clearly poisoned, and Alice did it. Gaius rounds on Merlin, telling him not to make accusations without proof. But he heads straight back to see Alice and tells her that he knows she did it. Alice is about to open up when Arthur, to whom Merlin has told everything, bursts in and arrests her.
Alice, tries to confess, but her throat becomes constricted and her eyes flash black. Merlin puts it all together, realising the poison is from the Manticore and that the creature is controlling Alice. Gaius tears through his books, looking for a cure. He discovers that the only way is to kill the Manticore by destroying its portal. The young warlock realises that the plan requires magic...from Gaius.
Merlin summons the Manticore and it immediately attacks the young warlock while Gaius begins incanting a spell. As the Manticore poises to strike, Gaius shouts the spell and the portal explodes. The Manticore disappears in a plume of smoke.
With the Manticore dead, the King makes a full recovery and sentences Alice to death. Gaius goes to see her and they reconcile their differences, declaring their love for each other. The warning bell sounds; a prisoner has escaped. Merlin knows Gaius must have helped Alice to escape. He wonders why he didn't go with her, but Gaius is resolute: who would look after Merlin, then?
Morgana and Mordred prepare to destroy Camelot (and Morgana plots to destroy Emrys). Is Merlin Camelot€™s last hope?
Merlin star Colin Morgan talks about the important events from episode 511 'The Drawing of the Dark.'
Mordred battles between his duty to his friends and that to his love, but is spared the choice.