Merlin and Arthur find themselves outnumbered in a bar fight but an enigmatic young man helps them win. The man’s name is Gwaine and he risks his own life to protect Arthur but during his act of bravery he is seriously wounded. The Prince decides to take him back to Camelot where he could make a recovery with Gaius' help. Gwaine immediately gets to work: drinking, flirting with the ladies and causing lots of trouble for Merlin who has been instructed to look after him. However, when two unscrupulous knights seem to plot to murder the Prince, will Merlin and Gwaine be able to stop them and save Arthur?

With Princess Mithian as the perfect bait, Morgana conjures a deception so powerful that the whole of Camelot is taken in - even Merlin himself. But as the storm clouds gather, will the young warlock see through the lies? Or will Morgana at long last fulfil her dreams of revenge?

High in the mountains, a great horde gathers; Morgana prepares for war with a vengeful Mordred at her side.

Merlin feels the weight of his destiny like never before as the ancient prophecies play out with terrifying accuracy. But before he can save his beloved Camelot, he must save himself. For it is not just the kingdom Morgana wishes to destroy – it is also Emrys.