High above the world, the Death Egg has returned. Dr. Eggman has seized control of the massive space station once again, using it as the heart of a new operation. Across the globe, his Badnik army has begun appearing in forests, mountains, cities, and ancient ruins, occupying everything in their path. Massive factories churn out more robots by the minute, while Metal Sonic leads Eggman's forces as his most trusted weapon. With Eggman's empire spreading faster than ever, Sonic, Tails, Knuckles, and Amy set out to stop him before the invasion reaches every corner of the world. The race to save the world begins once again.