Admiral Nelson becomes involved in a project to develop an amphibian adaption for man. He encounters conflict with the two chief scientists, rather than being cautious, both scientist want to rush ahead with research. Nelson worries what the emotional toll of the experiments may be.

When a missile is destroyed by apparent ultrasonic sound, the Seaview investigates with Adams, the mentally unstable launch commander, on board and finds an giant manta ray source which along with Adams' actions pose a threat to safety.