An army to fight. A demon to slay. A world to save. No pressure.

Old-school magic meets the modern world when young Alex (Louis Ashbourne Serkis) stumbles upon the mythical sword Excalibur. He soon unites his friends and enemies, and they become knights who join forces with the legendary wizard Merlin (Patrick Stewart). Together, they must save mankind from the wicked enchantress Morgana (Rebecca Ferguson) and her army of supernatural warriors.