Doctor Eggman opens an amusement park in space called Dr. Eggman's Incredible Interstellar Amusement Park, allegedly turning over a new leaf and making up for past transgressions. The park is made up of several planet-sized attractions. Suspicious, Sonic the Hedgehog and his best friend Tails investigate. They meet Yacker, who comes from a species of aliens known as Wisps. After Tails invents a translator to communicate with him, they learn that other Wisps have been enslaved by Eggman, who plans to harness their energy for a mind-control laser that will allow him to take over Earth.
Sonic proceeds to visit the planets, liberating the Wisps and shutting down the generators linked to the amusement park. He meets many of his friends along the way, who are also exploring the park in an attempt to disrupt Eggman's plans. After Sonic frees the Wisps, Eggman tries to fire the cannon at the world, but a piece of wreckage causes it to malfunction. As the amusement park begins to explode, Sonic confronts Eggman. Eggman uses the Nega-Wisps to power his final contraption, a robot that uses the powers of all the Wisps that Sonic has met against him. As the machine gets weaker, the Wisps escape and help Sonic defeat Eggman, sending him hurtling off into space. The Wisps carry Sonic out of the exploding amusement park. Returning safely to Earth, Yacker thanks Sonic and Tails.
However, Sonic and Tails soon learn that the leading Mother Wisp had been infected by the negative energy and transformed into the Nega-Mother Wisp. Using the power of the Chaos Emeralds, Sonic transforms into Super Sonic and fights her. Following her defeat, the Mother Wisp returns to normal and the Wisps part ways with the two heroes. In a post-credits scene, Eggman is seen stranded in space with his henchmen Orbot and Cubot.