An emergency space docking goes wrong and the core of the orbiting Spacehub transit terminal goes into meltdown. A young traffic controller named Conrad is trapped inside and Alan is unable to reach him. With Thunderbird 3 being used to keep Conrad alive International Rescue's only hope is to modify Thunderbird 2 for space flight in order to transport a new cooling system to the hub.
All of International Rescue take a retreat for training at their family ranch on the main island. During training the equipment malfunctions, MAX goes crazy and both the Thunderbird ships and FAB 1 stop working. John, Brains and EOS work together to trace the fault and discover that they have an intruder, The Mechanic!
The Tracys receive a distress call from the crew of a cargo zeppelin. A giant loading claw malfunctioned and has started attacking anything that moves. Thunderbird 1, 2, and Shadow launch out in an attempt to land the ship safely. But the zeppelin contains a dangerous fuel source and there are still crew members trapped near the loading claw. Scott makes it to the cockpit of the zeppelin while Virgil begins to offload the fuel source. Kayo puts on a mech suit to deal with the loading claw while the crew escape. Ultimately, they put the zeppelin down outside city limits and escape just before it explodes.
Gordon ventures deep into the Marianas trench to rescue a survey team, and ends up discovering an early International Rescue prototype vehicle once flown by Jeff Tracy. Gordon takes Thunderbird 4 down to save the crew and get a better look at the prototype. But the survey ship, designed by The Mechanic, transforms and wrecks Thunderbird 4. Gordon is forced to abandon ship and seek refuge on his dad’s TV-21 plane. To save the survey crew, Gordon powers up the plane and manages to take it up to the surface.
A geological survey team gets trapped when a huge earth-breaking vehicle, controlled by a villain known only as the Mechanic, causes them to fall into a narrow crevice. As International Rescue mobilise, Lady Penelope and Parker visit the Hood in Parkmoor Scrubs prison to find out more about this mysterious new villain.