Tom and Maddie let Sonic stay home while they're on vacation. However, Doctor Robotnik, now known as Doctor Eggman, escapes from the Mushroom Planet for revenge. He, along with his new partner, an echidna named Knuckles, search for a emerald with great power. It's up to Sonic, along with his newfound best friend, Tails, to stop the two before it's too late.