Watch Man from Atlantis

When a man who works in a carnival dies from drowning, Mark is sent to investigate. He learns that two men who work at the carnival are planning something that requires a someone who can hold their breath under water.

Mark believes a series of sonic "attacks" to be the song of a siren. He finds a young siren held prisoner on a submarine and must free her from the underwater pirates.

Disaster strikes at the Triton undersea habitat and threatens to spread to the world upon the appearance of Moby, a being that turns men's minds to those of a child.

Mysterious deadly canisters buried at the ocean floor resurface on a primitive island, where Muldoon has the natives believing he speaks for a powerful god.

An enzyme from a rock fossil Mark finds on the sea floor with the properties of changing people's personalities gets into C.W's coffee while Mark and Elizabeth are sent to recover a lost survey probe with a deadly self destruct booby trap.

When a sea quake opens a fissure and Mark investigates, he finds himself in the world of "Romeo and Juliet".

The Cetacean finds an underwater forcefield, which shelters a race of air-breathers with a strange clicking language. Mr. Schubert forces the Clicks to mine crystals for him, but taking the crystals will cause the field to collapse and kill them all unless Mark can intervene.

While investigating an underwater volcano, Mark is stricken with sudden pain in the shoulder. This is not the first time he's felt pain for no reason, and his instincts lead him to a deserted beach and, inexplicably, to a frontier town of the old west called Land's End. There he meets his identical twin, Billy, another water-breather who washed up on a beach with no knowledge of his true identity. Billy takes Mark's place aboard the Cetacean, leaving the Man from Atlantis to face the villains of Land's End.

Strapped for cash from his many expensive bids for world domination, Schubert breeds an aggressive genetically-altered jellyfish ten feet across named Poobah, and uses it for blackmail purposes. When the creature attacks a swim meet, Mark must battle the jellyfish.

The world is endangered when a vortex opens in the ocean, and Mark must find where its going and some how stop it before all the water is drained away.

Schubert's tracking of a mysterious power source causes a blackout, at the center of which, Mark discovers an ancient statue of a hawk. When he rescues Schubert's daughter Juliette from drowning, the villain learns of the hawk and steals it to discover the secret of its power.

Ships are being damaged by an unknown agent hidden at a depth impossible for the Navy to reach, where the Cetacean finds an automated robot, the Mud Worm. It is programmed to crawl along the sea bottom collecting mineral samples, but was damaged, and now resists all efforts to approach it with deadly force. Mark manages to shut down the robot and haul it inside the Cetacean, but when it reactivates, it will destroy everything in its path in an effort to escape.

Water levels are rising all over the Earth. Mr. Schubert offers to stop the disaster in exchange for Mark Harris, but it's the villain himself who is melting the world's ice caps with microwaves. Schubert agrees to stop the melt down if Mark will stay on of his own free will as a test subject, though his true plan is to flood the world and repopulate it with a new species of water-breathing men.