The Marios and Toad are trying to save the Princess from Koopa's riverboat. When their plan goes horribly wrong, Toad gets caught and the Marios barely escape with their lives. The Marios then meet up with Mark Twang, a man who's in a race with Koopa. The Marios and Mark now have to work together to beat Koopa and rescue Princess Toadstool and Toad.