Branded as a 'nerd' and harassed by the school bully, 12-year-old Arthur is rescued by a magical troll alchemist but is soon able to return the favor. Arthur's loving mom, who struggles to keep her devious ex-husband from gaining custody of Arthur, dismisses her son's 'fantasies' until she realizes their all-too-real immediate danger and joins forces with Arthur, the troll, the Knights of the Square Table (Arthur's pals Natalie and Tim), and Shane the washed-up inventor of a trading card game. Together, they hope to conquer a dragon and the wicked vice-principal who threaten civilization.