Undersea Girl (1957)

When the body of a fisherman is found beneath the sea, investigating police Lieutenant Mike Travis (Dan Seymour) persuades reporter Valerie Hudson (Mara Corday) to withhold the story. Later, a man arrested for fighting is found to possess $3,000 comprised of bills having the same sequence of serial numbers which were part of $2,000,000 lost when a naval ship was sunk, and the Navy assigns Lieutenant Brad Chase (Pat Conway) to the case. The investigation revelas that the money had been transferred from a trans-Pacific vessel to a tuna-fishing boat, then to an undersea cave by a gang of killers and thieves. Jealousy and distrust among the gang members result in aiding Brad to solve the mystery of the missing money. An undersea fight between the criminal and Brad and his skin-divers, including Valeria, leads to the trap Brad sets for their capture and the recovery of the money.