After a man washes up on the beach, doctors discover that he has gill-like tissues instead of lungs and amazing aquatic abilities.
EPISODE 1
Melt Down
Mark must surrender himself to Mr. Shubert to keep him from melting the polar ice caps.
EPISODE 2
The Mudworm
An invention designed to collect material from the ocean floor develops a mind of its own and threatens to destroy all sea life.
EPISODE 3
Hawk of Mu
Mark and Mr. Shubert's daughter recover a dangerous statue.
EPISODE 4
Giant
A whirlpool transports Mark to another world and he finds Muldoon trying to steal the gold from it.
EPISODE 5
Man O'War
Mr. Shubert tries to extort money by threatening to unleash a giant jellyfish on a swim meet.
EPISODE 6
Shoot-Out At Land's End
Mark is transported to the Old West and mistaken for an outlaw.
Alan Fudge
Patrick Duffy
Belinda Montgomery
Victor Buono
Ted Cassidy
Lee H. Katzin
Michael O'Herlihy
Harry Harris
Richard Benedict
Virgil Vogel
Charles S. Dubin
