Overview

Dr. Robotnik has stolen the Red Chaos Emerald, causing the other five to "lose balance" and scatter themselves into a parallel universe. As a result of the instability, South Island is now sinking into the ocean. It is up to Sonic and Tails to find the Chaos Emeralds and restore harmony to the universe, or else the innocent residents of South Island will find themselves taking a long swim.

Source: IGDB