A powerful underwater seaquake turns a busy day for International Rescue into a perilous one. While they attempt to rescue a research team trapped in an undersea lab, they quickly discovers a chain of seismic destabilisers positioned along the bottom of the ocean floor, and along the notable feature, "The Ring of Fire". Lady Penelope is quickly contacted to help the Thunderbirds find the person responsible, the Phantom figure known only as the Hood.