There's debate over who the rightful King of England is. King John fights a war with King Philip of France and takes his own nephew Arthur prisoner.
John's henchman tries and fails to blind and kill Arthur... but Arthur dies anyway in a freak accident. King John's nobles rebel against him and join forces with Louis, the Dauphin of France, who is invading England.
Commanded by the Bastard, King John's forces fight back against Louis and the rebel English nobles. The battle is inconclusive, but the tide turns in favor of King John when Louis's English allies turn against him and rejoin their king. The problem is, John gets poisoned by a monk and dies. Louis heads home, anyway. King John's son Henry is set to become the next king.