Dr. Deraad (Richard Coleman) finds out that the other saboteur is in fact Dr. Ellen Carey (Delena Kidd).  She blew up her own lab in order to divert suspicion away from her.  Now that International Metals is taking over the running of the drilling she no longer has to hide.

Mark Bannerman (Gerald Flood) convinces Captain Payne (Peter Williams) to make one last ditch effort to reach the x-layer of the seabed.  Despite not knowing the practical applications of the metal, Bannerman is convinced that the x-layer is Phenicium and the sabotage was done so that International Metals could get access to it.  International Metals is scheduled to take over the facility in twenty-six hours.  Bannerman suggests that the drilling be done non-stop and keep access to the drilling strictly controlled until the x-layer is reached.  If they can prove that the x-layer is Phenicium than the UN will keep control of the new metal.

When Dr. Carey finds out that the drilling has started again she needs to come up with a way to stop it.  Access to the drilling unit is tightly controlled.  She decides that the best way to stop it is to use Dr. Deraad.  She gives him a gun and tells him to confess to the sabotage in order to get access to not only Captain Payne but the drilling area in the blockhouse as well.  While he is in front of Captain Payne he is to use the gun to stop the drilling.

While Dr. Deraad is occupied with grandstanding, Dr. Carey sets off one more bomb.  This one traps, not only Deraad but, Captain Payne, Bannerman, Peter, and Professor Soobiah 35,000 feet down under the ocean.

Both “City Beneath the Sea” and “Secret Beneath the Sea” are geared a little more toward adults than the previous Pathfinder films.  The Pathfinder films are full of exciting adventures whereas the Beneath series are basically confined to the same cramped sets.  The underwater effect is heavy handed, the result of which makes it difficult to see what is going on. 

Despite the wonderful hammy acting of Aubrey Morris, I liked this series a little more than “City Beneath the Sea”.  Mainly because of the mystery element.  Still, both the Pathfinder and Beneath series have a wonderful charm to them.  The low budget sets are supplemented by interesting scripts and imaginative stories.  These are the stories that John Lucarotti and Malcolm Hulke learned their craft on before they graduated to “The Avengers” and “Dr. Who”.