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.

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.