When a mild earthquake hits, Harcourt Brown (George Coulouris) becomes trapped under some rocks that had fallen from the roof of the cave. Brown and Margaret (Hester Cameron) are cut off from Henderson (Gerald Flood), Mary (Pamela Barney), Wilson (Graydon Gould) and Geoff (Stewart Guidotti). A Venusian girl (Bridgid Skemp) appears and motions Margaret to follow her. The two make their way to the other side where they meet up with Henderson and the others. Everyone returns to where Brown is trapped. As lava is approaching from an underground volcano the group manages to free him just in time.
They find an exit from the caves and emerge on the other side of the mountains, near the city that Brown has been trying to get to. They can see the city glistening in the distance. Brown wants to head to the city but Henderson, now that they’ve found Wilson, wants to return to MR-4 so they can leave Venus and return to Earth. Eventually Henderson relents and says they need to rest for a while and then they will head toward the city. Being in a hurry Brown heads out ahead of everyone else.
While he is gone everyone rests by a pool of water. Margaret and Geoff discuss what to call their new native Venusian friend. They settle on Ki Ki, which seems to be the word she says the most. Mary falls asleep. When she wakens Henderson notices an insect bite on her face. She waves it off as being nothing. They head off toward the city.
The city that Brown was so intent on reaching turns out to be something far different than Brown expected. All of Brown’s hopes are dashed after he learns that the city isn’t a city after all – instead it’s a massive tomb where the Venusians bury their dead.
Mary soon becomes ill from the insect bite. The rest of the team must come up with a cure for her using the native vegetation.
Six of the “Pathfinders to Venus” episodes as well as all of the episodes of “Pathfinders in Space” and “Pathfinders to Mars” were directed by Guy Verney. The remaining two episodes of “Pathfinders to Venus”, this one and “Planet on Fire” were directed by Reginald Collin. This was Collin’s first directing credit.