While helping his former history professor search for pirate treasure off the North Carolina coast, Mike finds evidence that the underwater cave said to house the treasure has been tampered with.

A scuba diving ballerina faces the possibility of underwater amputation when she catches her foot between the buckled plates of a sunken freighter.

Mike scouts a path through mine-infested waters so that medical supplies can reach a China Sea port hit by a cholera epidemic.

Unaware that two of his treasure-hunting friends are trapped inside, Mike sets charges to blow up a sunken ship that is a menace to a busy shipping lane.

A man bribes Mike to continue giving lessons to an inept diving student whom he's stopped teaching.

Mike is trapped in a ""scubasphere"" when the cable attached to it snaps.

One salvage diver disappears while diving on a sunken yacht off the coast of Yucatan, and Mike tries to see that two others don't share his fate.

Mike poses as a tourist on vacation as he tries to locate a hidden underwater missile launcher in the Caribbean.

Mike uses sonar to foil a gang of underwater heroin smugglers.

A young Mexican boy helps Mike locate a safe entrance to an underwater fossil cave.

Mike convinces a reluctant daughter to continue her father's work after he is killed testing an underwater electrical detection device.

Mike is hired by a local German consul to salvage a survival kit from the wreckage of a Nazi warplane in the Caribbean.

A sunken truck points Mike to the murder of a political boss, and the killer is the father of a good friend of Mike's.

A heroic test pilot from the Korean War has his mettle tested when he must spend 24 hours with Mike in a makeshift decompression chamber after a dive to prevent the bends from killing him.

While searching a Latin American harbor for a sunken statue, Mike discovers a UHF homing beacon being used to guide submarines into the port.

A naval officer of a Caribbean nation is sabotaging a series of experiments Mike is conducting with the Coast Guard.

Mike investigates the source of a radar jamming signal that caused two ships to collide.

Mike's efforts to retrieve a pair of radioactive cylinders are complicated by the presence of a headstrong youth to whom he's been giving diving lessons.

Mike heads a three-man team in an effort to disarm a pair of unexploded torpedoes at the bototm of a West Coast harbor.

While on a diving expedition in Guatemala, a woman seeking to slow down her husband's frantic lifestyle deliberately sinks the boat they share, unaware that her husband is a diabetic and his insulin supply will be lost with the vessel.

Mike's assistant is trapped underwater by an overturned truck containing drums of poison that could endanger a South American city's water supply.

Mike helps test a remote control guidance device invented by a rich eccentric.

During hydroplane races, a friend of Mike's rams his craft into a Coast Guard ship, leaving Mike to investigate.

Mike helps the daughter of his old UDT Commander investigate the man's death, which she believes was murder.

Markings on the body of a dead diver convince a marine biologist that a tropical lagoon is inhabited by a killer octopus.