Sonic Chronicles: The Dark Brotherhood

The game initially focuses on the events surrounding the kidnapping of Knuckles and the disappearance of the Chaos Emeralds after the defeat of Doctor Eggman, before moving on to follow the cast of characters across two dimensions as they encounter a new ally, Shade the Echidna, and seek to stop the invasion of their world by Ix, the leader of Shade's tribe, the Nocturnus.