Big Nick is back on the hunt in Europe and closing in on Donnie, who is embroiled in the treacherous world of diamond thieves and the infamous Panther mafia, as they plot a massive heist of the world's largest diamond exchange.

Sonic, Knuckles, and Tails reunite against a powerful new adversary, Shadow, a mysterious villain with powers unlike anything they have faced before. With their abilities outmatched, Team Sonic must seek out an unlikely alliance.