Steve is assisting scientist Dr. Louis Craig and Sharon Ellis in placing earthquake sensors on the ocean floor when they receive word that the nearby country of Santa Ventura has broken off diplomatic relations with the United States. They are warned to leave the area, but before they can retrieve Steve's diving bell from the depths, a patrol boat captures the ship and the air hose to the diving bell is severed. Steve manages to escape, swims to shore, gets help from a local rebel, poses as a soldier, and rescues Craig and Ellis.