The Frost Line Outer Space Defence System is a network of missile bases in Northern Canada, tasked with protecting Earth from extraterrestrial threats. In a transmission to Earth, the Mysterons (voiced by Donald Gray) warn Spectrum that they intend to attack key Frost Line installations. They use their powers to destroy a snowcat driven by maintenance technician Eddie and reconstruct both Eddie and the snowcat as agents in their service. The reconstructed Eddie passes security at two bases – Red Deer and Cariboo – and plants devices inside their ventilation systems that render the air unbreathable, killing 250 personnel at Red Deer and 70 at Cariboo.