In the inky depths of an ancient pool, three soothsayers cast a dark judgment upon the king of Camelot. But despite Merlin's warnings, headstrong Arthur refuses to take the words of the Disir seriously, and their fury rains down on Camelot. Only the greatest sacrifice can appease them, and with the kingdom in jeopardy, is it one that Arthur is prepared to make? Faced with the king's uncertainty, Merlin has just one chance to save him from his destiny - but this decision comes at the highest price.

Cast: John Hurt, Angel Coulby, Adetomiwa Edun, Tom Hopper, Bradley James, Eoin Macken, Katie McGrath, Colin Morgan, Helen Schlesinger, Sian Thomas, Andrew Tiernan, Frances Tomelty, Alexander Vlahos, Richard Wilson, Rupert Young