On a recon mission with the new Diamond Cutters--Tangle, Whisper, and Lanolin--Sonic discovers that the Eggperial City is harnessing the resources around it to grow ever larger. The Diamond Cutters are still getting the hang of working together which leads to trouble when they get trapped. Alone against an army of badniks and a self-replicating city, Sonic calls for back-up and gets more than he bargained for: Tails, Amy, Blaze, and Silver all answer the call, but Shadow, Rouge, and Omega arrive for their own reasons too! While the Diamond Cutters have to have an emotional break-through to escape, Sonic and Tails coordinate a horde of heroes to try to bring the city down!