The young Arthur runs the back passages of Londonium with his crew, not knowing his royal lineage until he grabs Excalibur. Instantly confronted by the sword’s influence, Arthur is forced to make up his mind. Throwing in with the Resistance and an enigmatic young woman named Guinevere, he must learn to master the sword, face down his demons and unite the people to defeat the tyrant Vortigern — who murdered his parents and stole his crown — and become king.