A Soviet cargo ship carrying medical opium gets attacked by pirates of an unknown nationality. The crew is left to die on a sinking ship but they manage to escape and now must fight the pirates for survival.
While doing their work on the deep underwater station two aquanauts discover strange mystery: it seems as if one of the aquanaut's girlfriend who recently died in a car crash had turned into a big manta fish. That manta writes words on the station's port-holes and tries to draw attention many other ways.
