When a stranger gives Arthur the power to summon the dead, the king finds himself torn between head and heart. Unable to resist temptation, he seizes the chance to speak to the person he misses most - his father, Uther. But the spirit world is a dark and dangerous place... Little does Arthur realize that his decision comes at a terrible price. Against all odds, Merlin must put right Arthur's mistake before Camelot and everything they have built is destroyed forever.

Cast: Angel Coulby, Adetomiwa Edun, Anthony Head, Tom Hopper, John Hurt, Bradley James, Eoin Macken, Katie McGrath, Colin Morgan, Gordon Munro, Sophie Rundle, Julian Seager, Jane Thorne, Alexander Vlahos, Richard Wilson