Bayard and the knights of the Western Isles are welcomed to Camelot for a feast celebrating a union between the two kingdoms, as BBC One’s adventure-packed family drama continues. Nimueh, however, has other plans. Posing as a serving girl, she infiltrates Bayard’s party and enters Camelot with a view to seeking revenge on Merlin.

Unaware of her true identity, Merlin befriends the young serving girl. Once she has gained his trust, Nimueh warns him that Bayard isn’t the friend he seems as he plans to poison Arthur.

Merlin bursts into the banquet and stops Arthur drinking from a poisonous goblet in the nick of time. Bayard denies trying to poison Arthur and Uther decides that the only way to determine the truth is for Merlin to drink from the cup himself. Merlin falls to the ground, poisoned. The guards arrest Bayard and his knights. Merlin falls into a deep coma.

Gaius discovers that Merlin has been poisoned by the Morteaus Flower and can only be saved from certain death by an antidote made from the leaf of the same plant. However, the flower is rare and only grows in the caves of Mount Argeaus, which are found deep within the forest of Balor. As Merlin’s health deteriorates fast, Arthur, humbled by his servant’s bravery, believes he must set off on a quest to retrieve the flower himself. But Uther forbids him to go because the danger is too great.

Morgana counsels Arthur and helps him realise that he is his own man and should do what he thinks is right, even if it means disobeying Uther. Will Arthur find the flower in time to save his friend or will Nimueh place more danger in his path?

Saturday 11 October
7.05-7.50pm BBC ONE