Sonic, Tails, Knuckles, and Sally Acorn head to a new island called the North Star Islands, where they discover the nefarious Dr. Robotnik is once again converting animals into Badniks and trying to take over the world, this time while even converting giant animals into Super-Badniks as well seeking a mysterious dark force within the islands to assist his latest plot. With all these new threats in their way, it's up to Sonic and his friends to free the animal friends once more, explore the mysterious Northstar Islands alongside its secrets, and stop Robotnik's latest plan of world domination.