We join Arthur and Merlin just weeks after Arthur has been crowned King of the Celts (the climax of the first film). However the Celtic Chieftains dismiss him as an illegitimate king and descend on the Celtic fortress of Dinas Affaraon to overthrow him. They offer Arthur a chance to prove himself. If he can defeat the greatest warrior from each tribe in one-on-one combat, he will retain the crown. But the contest is interrupted by the arrival of Balor, a vengeful thief who has been bestowed with a terrifying evil power by the dark gods of the underworld who want to transform the Celtic kingdoms into a land of darkness. Arthur has no choice but to recruit the help of the very warriors who came to topple him. With Merlin his only ally, the young king must lead this rag-tag band of feuding warriors on a quest to hunt down Balor before he destroys everything they have fought to protect.