Joe Cornish writes and directs this fantasy adventure drama based on the legend of King Arthur. School boy Alex (Louis Ashbourne Serkis) is fed up of being picked on by bullies at his school. Everything changes however when one night, while being chased by the bullies, he encounters the sword of Excalibur. Alex at first doubts its origins, but when Merlin (Angus Imrie/Patrick Stewart) arrives he soon learns the truth about the sword and his own destiny. Meanwhile, the powerful sorceress Morgana (Rebecca Ferguson) is clawing her way back to the land of the living which spells disaster for the world and it is now up to Alex and his unlikely band of fellow knights to put a stop to her before it's too late.