Princess Peach discovers a mysterious map that sets her on a quest to uncover the secrets behind the Thousand Year Door, a legendary entrance to a hidden world. According to legend, the door was once buried by an ancient city, only to be rediscovered and covered by another civilization. Theories abound about what lies beyond the door, but Peach is determined to find out.
The journey begins in Rogueport, where Peach sends a message to Mario, inviting him to join her on this perilous quest. Upon arrival, Mario meets Goombella, a charming female goomba who joins forces with him. Together, they seek out the expertise of Professor Archeology, who agrees to guide them to the Thousand Year Door. As they approach the entrance, the map reveals the locations of hidden stars, and the adventure commences.
Players control Mario as he explores various lands, battles enemies, and collects allies to aid him in his quest. In battle, the outcome is decided by executing action commands on a stage in front of an audience. The crowd's mood can shift quickly, with some members cheering or throwing objects at Mario. At these moments, players must intervene to restore order.