Phones and Lt. Fisher are assigned to Denver's crew. When a storm hits, Denver is knocked out and loses his memory and Phones and Fisher are cast adrift in a small dinghy. Troy, however, succeeds in overpowering Denver who later regains his memory in hospital. X20 has planted a bomb in the bass fiddle of a jazz group that will give a concert at the undersea city of Aphony, Marina's father.
Troy uncovers the plot but is trapped in a burning shack.
He escapes just in time and races to Pacifica in Stingray in an attempt to save the lives of his friends. Fisher takes command of Stingray in his training to become an Aquanaut. The exercise involves target practice on a Terror Fish target but X20 has attached a sticker bomb to one of the targets and one to Stingray's hull. Troy is air-dropped into the sea in an attempt to remove the bomb from Stingray's hull before it explodes. While trying to decide what to wear to Atlanta's fancy dress ball, Troy falls asleep and dreams that he and Phones are pitted against a race of underwater cavemen who plunder the cargo of a vessel varrying radioactive material.