It was an official test run..nothing dangerous, nothing unplanned. Just a chance to show the brass and the press how the new atomic sub Triton took the depths. Don Miller was thrilled to be aboard. It was the chance of a lifetime, and he wouldn't have missed it for the world. But at 500 fathoms, there was trouble with the tanks; at 700, there was even more..and there was a limit to the pressure even a sub like the Triton could take. Suddenly it became obvious that things were not happening accidentally, that at a depth never before possible for a man to reach, the Triton was being sabotaged!