The final lost world movie that director Kevin Connor and actor Doug McClure made together in the late 1970s was this original tale of the search for the lost city of Atlantis.

The first three collaborations were all Edgar Rice Burroughs adaptations but for this film they hired screenwriter Brian Hayles who wrote several Doctor Who episodes in the 1970s.

On the ship the Texas Rose archeologist Professor Aitken (Donald Bisset) and his son Charles Aitken (Peter Gilmore) are looking for the lost city of Atlantis but haven’t informed the crew that’s what they are looking for. Greg Collinson (Doug McClure) has helped the Professor design a diving bell to search and Greg and Charles go down into the ocean to search.

They are attacked by a giant sea monster which they manage to fight off and find a giant gold statue. They bring the statue to the surface but the ship is attacked by a giant octopus. Some of the crew are taken by the octopus along with Charles and Greg. They are brought to an underground cavern that has air. There they are met by Atlantean guards who inform them there are seven cities of Atlantis and take them Vaar, the fourth city. While the rest of the group are imprisoned Charles is taken to Chinqua, the fifth city where he meets Atraxon (Daniel Massey) and Atsil (Cyd Charisse), the king and queen of Atlantis. They inform him that they are originally from Mars and offer to make him one of them because of his scientific knowledge. They then inform him of how they want to change the Earth.

Meanwhile Greg befriends some of the other prisoners including Delphine (Lea Brodie) whose father is the captain of the Mary Celeste. The Atlanteans want to change the prisoners so they can breath under water and force them to fight the giant evil Zaargs (big monster lizard creatures) who constantly attack the cities. Greg and company try to escape, free Charles and along the way fight Zaargs, Atlanteans and flying piranha fish things. Oh and the giant octopus.

The movie is just as silly as the last three movies in the lost world series that director Kevin Connor made. All the films are way more ambitious than their budget and by the time they made this film Amicus Productions, who made the first three had gone bankrupt. Still it’s a stupid fun film and the monsters are pretty decent looking, still using the puppet technique but it kind of works. For whatever reason the movie was renamed Warlords of the Deep for the U.S. release.