King Arthur returns home after fighting the Roman Empire. His illegitimate son has corrupted the throne of Camelot and King Arthur must reunite with the wizard Merlin and the Knights of the Round Table to fight to get back his crown.
An outlaw named Guerrero Hernandez is shot in the back and killed whilst attempting to free his half-brother from a small-town prison. Making a deal with the devil, Hernandez returns from the dead to take his revenge.
During a handover to the head of counter-terrorism of MI5, Harry Pearce, a terrorist escapes custody. When Harry disappears soon after, his protégé is tasked with finding out what happened as an impending attack on London looms, and eventually uncovers a deadly conspiracy.