The scientific crew on the Orpheus submarine runs into severe danger in their quest to find rare micro-organisms. One crew member has died, the Orpheus has been intercepted and two of the crew are trapped and running out of air. They have to escape, but can they risk boarding the mysterious vessel which looms above them?

The Orpheus is mended, and the captain wants the crew to find more of the rare bio-fuel samples before they return to the surface. The Russian captain has other ideas, however, and instructs his men to kill the crew. In their struggle to escape, some are left behind; will they be able to complete their mission?