A man stricken with nitrogen narcosis disappears into a shapeless eerie ocean mass. Primus swims to investigate. An ex-frogman(Dan Chandler) is dying in an underwater habitat. The only doctor who can perform a tracheotomy to save him, has never made a descent. Carter Primus (Robert Brown) and Charlie Kingman (Will Kuluva) guide the doctor (Mike Road) 320 feet undersea, but the doctor develops nitrogen narcosis and Primus must perform the tracheotomy himself.