The game takes place on the tropical resort of Isle Delfino, which is shaped like a dolphin and comprises ten primary locations. The island is mainly inhabited by the races Piantas and Nokis.Delfino Plaza is Isle Delfino's capital and the game's main hub. Mario sets out for Isle Delfino for a vacation with Princess Peach, her long-time steward Toadsworth, and some other Toads, hoping for a relaxing vacation. Upon arrival, they find that the once-pristine island has been polluted and plastered with graffiti. As a result of this pollution, sun-shaped objects called "Shine Sprites", the island's sources of power, have disappeared, and the island is covered in a perpetual shadow. The culprit seen spreading the graffiti is disguised as Mario (referred to as "Shadow Mario"). Mario is promptly arrested as he arrives, falsely accused of vandalizing the island. He is put on trial, found guilty, and ordered to clean up the graffiti and recover the Shine Sprites. To help with the cleaning, Mario finds FLUDD, a powerful water cannon which is toted like a backpack. Mario sets out on an adventure to clear his name and locate the real criminal, while restoring tranquility and order to Isle Delfino.