 Submarine pilots Osborne (Ronn Carroll) and Hodges (Thom Bray) send an unmanned probe to explore, but lose contact and venture in after it.Upon finding the probe, they detect a large sonar contact moments before being attacked and killed by an unseen force.The unseen aggressor then attacks the observation pod, leaving Joyce Collins (Nancy Everhard) and a dying Burciaga trapped inside as it teeters on the edge of the ravine.