Four men, a woman and her child are rescued by Captain Nemo (Robert Ryan) when their ship – en route from London to America during the civil war – sinks during a storm.
The survivors are US Senator Robert Fraser (Chuck Connors); widow Helena Beckett (Nanette Newman); her young boy, Phillip (Christopher Hartstone); a twitchy claustrophobic chap named Lomax (Allan Cuthbertson); and two bumbling crooks – Barnaby (Bill Fraser) and Swallow (Kenneth Connor) – who provide the film’s comic relief.
Nemo takes the survivors to his utopian domed city 10,000 fathoms below the surface of the sea and won’t allow the new arrivals to return home to the surface for fear that they will reveal the existence of his amazing metropolis to the warring nations above.
Senator Fraser becomes involved in a romance with Mala (Lucianna Paluzzi), which enrages Joab (John Turner).
Nemo becomes a kindly father-figure to young Phillip and develops a close friendship with the headstrong Helena. Eventually offered the choice to betray Nemo and leave the undersea city, or stay with Nemo and form an ad hoc family, Helena chooses to remain.
Meanwhile, a giant manta ray named Mobula threatens the city until Fraser becomes a hero after dispatching the murderous beast while in command of Nautilus.
But Fraser is plotting to escape aboard a brand new Nautilus #2 with the help of the treacherous Joab and the avaricious Barnaby.
Senator Robert Fraser
John J. Moore