The game's action unfolds in the world of King Arthur: Knight's Tale — a dark version of King Arthur's universe. A new threat looms over Avalon: the infamous Ninth Legion, led by the fallen hero Gaius Julius Menton, has invaded the mysterious island. Menton seeks a way to escape from Tartarus on the orders of the deceased Emperor Septimius Sulla. When the demonic warriors enter the magical kingdom of the Lady of the Lake, Gaius Julius Menton decides to seize the island and establish Eternal Rome. However, first, he must gather the lost legion.