Might and Magic: Book One is the first dungeon-crawling role-playing video game in the long-running series. The plot focuses on six adventurers in a quest to discover the secret of the "Inner Sanctum," though little information is offered upfront about this quest or its object. The ultimate quest is kept intentionally vague, and left for players to gradually piece together as they explore the world.

Although the game appears to take place in a straightforward medieval fantasy setting of knights in armor, mythical monsters and magicians, a number of science fiction elements are revealed later in the game.