A powerful seaquake turns a busy day for International Rescue into a perilous one. Lady Penelope helps Thunderbirds find who put seismic destabilisers on the sea bed.

John and Brains must track down the source of the seismic destabilisers. Meanwhile Scott and Virgil race to Taiwan when one of the undersea quakes destabilizes a solar collector dish in Taipei.

Alan is on space junk duty, when one of the pieces of debris turns out to be a heat-seeking SAT-MINE that activates and locks onto TB3's heat signature. Back on Earth, Lady Penelope and Parker implement a plan to sneak into a top-secret storage facility.

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.

Kayo is riding aboard Fireflash, a supersonic airliner invented by Brains, but she is unaware that its controls have been tampered with. International Rescue notices the plane has vanished from their monitors and attempt to locate it. Kayo realises that the plane is flying in the wrong direction, and manages to avoid a powerful gas attack that has knocked out both passengers and crew.

Virgil and Brains attempts to rescue a mining crew trapped inside a glacier, but the scientist in charge of the project refuses to leave.