Bardon Pass is attacked and Arthur and his men rush to protect it. Merlin discovers Morgan has been in the castle all this time.

Cast: Joseph Fiennes, Jamie Campbell Bower, Tamsin Egerton, Claire Forlani, Peter Mooney, Philip Winchester, Eva Green, Sinéad Cusack, Tyler Kennington, Darryl Kinsella, Diarmaid Murtagh, Conor O'Gorman, Sebastian Spence, Clive Standen