When Thunderbird 5 picks up an unusual radiation spike from a remote corner of Africa, John discovers a former uranium mine has reopened, leading to Scott rushing there in Thunderbird 1 to investigate, with Virgil following. When Scott arrives and enters the mine, he discovers a source of unstable uranium, and is attacked by a mysterious woman, who claims that the mine belongs to her family. During their confrontation the mine soon begins to crumble, and she and Scott must work together to escape and reseal the mine, before a storm spreads the leaking radiation to the nearest city with serious consequences.