Mario is having a vacation in Dinosaur Land when he learns that Princess Peach Toadstool has been kidnapped by the evil King Koopa Bowser. When Mario starts searching for her he finds a giant egg with a dinosaur named Yoshi hatching out of it. Yoshi tells Mario that his fellow dinosaurs have been imprisoned in eggs by Bowser's underlings. The intrepid plumber has to travel to their castles, rescue the dinosaurs, and eventually face King Koopa himself, forcing him to release the princess.