A young druid called Daegal (Alfie Stewart) seeks Merlin’s help in curing his ailing sister. Hoping Arthur will not notice his absence, the warlock sets forth with Daegal to the Valley of the Fallen Kings, a half-day’s journey from Camelot.
Back at the citadel, Arthur prepares to sign a peace treaty with the fearsome Sarrum of Amata, but he is unaware that Morgana and Gwen are planning to enlist Sarrum into their latest plot to kill Arthur.
As night falls, Merlin discovers that Daegal is actually working for Morgana. After falling into a trap, Merlin is knocked out, poisoned and left to die in a ravine.
Back at Camelot, Arthur and Gwen dine with Sarrum who recounts how he imprisoned Morgana in a pit for two years with only a dragon for company. Gwen later meets with Sarrum and offers him a third of Camelot’s lands in return for Arthur’s head. Sarrum agrees, but secretly he plans to do away with Gwen as well.
Back in the forest, a guilty Daegal comes to Merlin’s aid and gathers the herbs needed for an antidote to the poison. Once revived, Merlin races back to the citadel with Daegal in tow.
During the signing of the treaty, as Sarrum’s assassin takes aim at Arthur, Merlin manages to redirect the arrow towards Sarrum, killing him. Daegal, however, is fatally wounded during the fracas, but dies a hero.
The episode ends with Merlin keeping quiet once more about Gwen being in league with Morgana. But now that the puppet queen knows that Merlin is onto her, what will she and Morgana come up with next?