Rupert 'Wolf' Wolfsen works for the US government, he is liaising with the US military in central America to help find a suitable cave where they wish to instigate a new top secret radio device for submarines?. They have trouble finding such a location until after a large landslide an entrance to just such a cave reveals itself. After setting up their equipment, they retire to base camp only to find that when they return the next morning, their irreplaceable transmitter has been taken and the guards dead. A search and rescue mission is authorised to go into the furthest reaches of the cave. Preposterous premise aside this was rather good fun, What Waits Below can only be described as a cross between Marshall's The Descent and Universals The Mole People, right down to the latter's albino civilisation who live there. Don Sharp just about retains an air of quality to proceedings, there may even be some pseudo political message in the ending.