The followup to Ecco the Dolphin. Ecco successfully destroyed the Vortex, but the Vortex Queen followed it to the earth and eventually destroyed the Asterite. The whole ocean is threatened, and actually already doomed.
In order to restore the Asterite and finally defeat the Vortex Queen, Ecco will have to confront again the tides of the time, which has split into two possible futures, the regular one and the dark one dominated by the Vortex Queen.
Ecco 2 features even better graphics than its prequel, and introduces a new gameplay mode in which the camera follows the dolphin from behind instead of from the side.