After Jimmy Wedgwood (Richard Dean) falls down an air shaft on the surface of the Moon he finds what appears to be an alien spacecraft. Conway Henderson (Gerald Flood), Geoffrey Wedgwood (Stewart Guidotti) and Valerie Wedgwood (Gillian Ferguson) climb down the shaft and examine the cave structure where the spacecraft is.
When Conway accidently adjusts a valve on the airshaft the vibration causes a small landslide that blocks the exit. The team finds some alien writing and a set of large doors but they have no way of opening them. Conway and the kids are running out of air and are stuck underground with no way to contact Professor Wedgwood (Peter Williams) or the other team members of MR-1.
Professor Wedgwood and the team of MR-1 have figured out that the symbols carved in the lunar rock are directional indicators. They follow them and find MR-2 but no one is aboard the rocket. They set out looking for Conway and the children. They eventually find the underground cavern just in time to save everyone. Professor Wedgwood determines that the cavern is airtight. They decide to use the cavern as lunar base one and begin studying the symbols on the walls.
Jimmy wanders off looking for Hamlet, his guinea pig. Valerie grows concerned and goes looking for him. What she finds is not of this world. Her screams can be heard throughout the cavern.
The Pathfinders series was broadcast as part of ITV’s Sunday Family Hour. ITV is a British free-to-air television network. It was launched in 1955 as Independent Television, a television station in competition with BBC Television.
Richard Dean, who plays the younger brother Jimmy Wedgwood in the series, was actually older than Stewart Guidotti, the actor who played the older brother Geoffrey Wedgwood. Stewart would go on to play Geoffrey in the two sequels “Pathfinders to Venus” and “Pathfinders to Mars”.