The treacherous Darkhouse, lurking in the Abyss, wants to expand its empire across the vast oneiric ocean. To enact its wishes, it has sent its infamous henchman, the Phantom Submarine, to enslave the Happy Isles. The only way to put a stop to this is to face the Darkhouse itself with a Nautilion submarine and a complete crew of heroes before the Phantom Submarine reaches its destination!