The Venture, an old trident nuclear submarine retrofitted for research, has picked up an ancient and powerful artifact off the ocean floor and brought it aboard. Called the Hades Stone, it allows the dead to pass through a portal into the world of the living. No one has entered the portal, but evil things have emerged: phantoms, demons, and an ancient being known as the Stone Keeper, guardian of the Hades Stone. The Stone Keeper and his stone demons promptly attack, killing the entire crew and commandeering the submarine. Now, it is up to the elite Phantom Force team to stop him.