From cover Deep beneath the surface of the oceans order is maintained by the dedicated submarine pilots if the Aquanaut patrol. In their sleek, deadly craft, armed with torpedoes and depth-charges they were incincible - until they met the challenge of the Caves of Shallic. Here were gathered the forces of a malevolent power, bent on conquest of the seas. Heat-seeking missiles, sea-tanks, hovering mine-layers, and worst of all, the lethal hunting mines. These could not be destroyed except by causing them to collide with solid rock. However their range was limited and they could be outrun by skilled pilots. There weapons had destroyed all but one of the Aquanauts. Could he penetrate to the deepest cavern, and survive to return to his base?