As the team continue their quest to save the researched, Lady Penelope is on the trail of their adversary.

Thunderbird 5 picks up an unusual radiation spike from a remote corner of Africa, and Scott rushes in with Thunderbird 1 to check it out. Using special equipment, Scott enters the mine and discovers the source to be a leak of unstable uranium. Moments later he is attacked by a mysterious woman who claims that the mine belongs to her family. During their confrontation, the mine begins to crumble - and Scott and she must find a way out.