The Striker Force dives underwater and meets Ariel, an old friend of Andrew who is fascinated with the world above the surface. After a bitter confrontation with her father King Triton for saving a human prince, Ariel strikes a bargain with the sea witch Ursula to become human for three days. Now the Strikers must help Ariel win the prince's heart before the three days are up.

Rock band StarSound is called back to perform their heroic duties when a new threat from outside the galaxy plans to invade Earth. Only the power of three relics can save the universe from total annihilation.