A mysterious enemy is inflicting havoc on Angel Island. Knuckles has been kidnapped and all but one of the Chaos Emeralds has been taken. Now it's up to Sonic and his team of friends - including Tails, Amy, Shadow and Knuckles - to set out on a quest to stop this new threat from another world. Their adventure takes them away from their home in the Green Hill Zone to Angel Island and through to an alternate and terrible dimension. Sonic and his friends must combine their skills and strengths to overcome all obstacles and evil enemies in their biggest challenge yet.