After saving Eri and taking down Overhual, Sonic and the rest of 1-A begin their next assignment; running a mock hero agency on Nabu Island. However, things don't go as planned as Dr. Eggman announces his grand return, promising to conquer the world in no less than 3 days. Team Sonic is on the job, but now all the others want a crack at the action as well, and with all of 1-A racing for the doctor, who will reach him first and thwart his scheme?