1x1 - Melt Down

September 22, 1977

Schubert threatens to cause worldwide flooding by using powerful microwaves to melt Earth's polar ice caps, unless the government turns Mark Harris over to him.

1x2 - The Mudworm

October 13, 1977

When a multimillion-dollar underwater probe malfunctions and begins attacking any ship that travels near it, Mark must reason with its highly advanced brain and convince it to stop.

1x3 - The Hawk of Mu

October 18, 1977

Mark, investigating a power outage, discovers a centuries-old hawk statue from the legendary civilization of Mu. The statue, when used properly, can remove the power from a large area. Schubert discovers the power of the hawk statue and Mark must prevent him from taking it.

1x4 - Giant

October 25, 1977

The oceans are leaking through a fissure in the ocean floor. A con-man named Muldoon agrees to guide Mark through the fissure to investigate. However, Mark is unaware either that giants inhabit the other side of the fissure or that Muldoon has already stolen gold from one of them.

1x5 - Man O' War

November 1, 1977

Schubert threatens to cause worldwide flooding by using powerful microwaves to melt the earth's polar ice caps, unless the government turns Mark Harris over to him.

1x6 - Shoot-Out at Land's End

November 8, 1977

When a multimillion-dollar underwater probe malfunctions and begins attacking any ship that travels near it, Mark must reason with its highly advanced brain and convince it to stop

1x7 - Crystal Water, Sudden Death

November 22, 1977

Mark, investigating a power outage, discovers a centuries-old hawk statue from the legendary civilization of Mu. The statue, when used properly, can remove the power from a large area. Schubert discovers the power of the hawk statue and Mark must prevent him from taking it.

1x8 - The Naked Montague

December 6, 1977

The oceans are leaking through a fissure in the ocean floor. A conman named Muldoon agrees to guide Mark through the fissure to investigate. However, Mark is unaware that giants inhabit the other side of the fissure and Muldoon has already stolen gold from one of them.

1x9 - C.W. Hyde

December 13, 1977

Using his genetic scientists, Schubert produces a giant jellyfish which he intends to release unless his extortion demands are met.

1x10 - Scavenger Hunt

April 18, 1978

Mark is somehow linked with a man named Billy, existing in a wild west town, who appears to be his twin. Investigating, Mark arrives in the town and discovers Billy had the same webbing as Mark but has had it removed.

1x11 - Imp

April 25, 1978

Schubert attempts to make a satellite weapon to knock out the Earth's communications. However, to power the weapon he needs the energy crystals protected by a forcefield under the ocean. The crystals actually power the forcefield that protects an underwater city.

1x12 - The Siren

May 2, 1978

An underwater landslide transports Mark to Verona, Italy... in the days of Romeo and Juliet.

1x13 - Deadly Carnival

June 6, 1978

C.W. develops a Jekyll-and-Hyde personality after swallowing a mysterious liquid.

Patrick Duffy

Mark Harris

Belinda Montgomery

Dr. Elizabeth Merrill

Alan Fudge

Dr. Crawford