In 2068, the New World Aircraft Corporation in England gives Brains [David Graham] a bold brief to design a revolutionary aircraft. Brains suggests an airship, prompting laughs from the executives, but his proposal is ultimately approved and the corporation unveils Skyship One — a fully automated craft powered by an anti-gravity field. Representing International Rescue for the maiden voyage — a round-the-world trip with computer‑programmed stops — are Alan Tracy [Matt Zimmerman], Tin-Tin Kyrano [Christine Finn], Lady Penelope Creighton-Ward [Sylvia Anderson], and Parker [David Graham]. Brains is forced to remain on Tracy Island after Jeff Tracy orders him to design a sixth Thunderbird machine. Working without a formal specification, Brains comes up with a range of concepts, yet Jeff rejects them all.
Alan Tracy [Matt Zimmerman] and Tin-Tin Kyrano [Christine Finn] fly to England in Alan’s restored Tiger Moth biplane, where they reunite with Penelope and Parker and the four of them board Skyship One. As the airship departs, the crew remains unaware that Captain Foster [John Carson] and the ship’s stewards have been murdered and replaced by The Hood’s agents, now operating as Black Phantom [Gary Files] from an abandoned airfield near Casablanca. Because the ship is automated, the impostors don’t need any technical know-how and can keep the guests in the dark.
After Skyship One sails past the pyramids of Egypt, Penelope discovers a bugging device in her bedroom. Foster and his men have been recording and editing her voice to craft a phony radio message urging Jeff to send Thunderbirds 1 and 2 to the airfield, where The Hood and his men plan to capture the two craft. Parker uncovers the editing gear, but before anyone can act, the impostors complete the message and transmit it to Tracy Island via Thunderbird 5. Jeff immediately dispatches Scott [Shane Rimmer] and Virgil [Jeremy Wilkin] in Thunderbirds 1 and 2, but Alan realizes his brothers are walking into a trap and Penelope manages to relay the warning just in time. When Skyship One lands at the airfield, Scott and Virgil unleash the Thunderbird rockets to wipe out The Hood’s base and then hurry to rendezvous with Skyship One.
Onboard the airship, the guests engage the impostors in a tense shootout. Tin-Tin Kyrano [Christine Finn] is taken hostage, forcing surrender. During the chaos, the anti‑gravity system is damaged, and the ship begins to lose altitude, crashing into a radio mast at a missile base near Dover. With Skyship One balanced precariously on the mast and its anti‑gravity field faltering, the rescue falls to Scott, Virgil, and Brains to save everyone before the craft topples onto the base below. Because there is no suitable Thunderbird 2 pod vehicle light enough to reach, Brains volunteers to pilot a risky rescue from the top deck. He flies a Tiger Moth up to the airship’s deck, but Foster captures him at gunpoint. Penelope is held hostage in the cockpit as Foster attempts a desperate takeoff, only to be shot dead by Alan. The Tiger Moth then launches with the guests and impostors clinging to the wings and landing gear. Skyship One crashes to the ground, triggering a chain reaction that obliterates the missile base.
The remaining impostors meet their end in a gunfight aboard the Tiger Moth. Stray bullets puncture the fuel tank, forcing Penelope to execute an emergency landing. After near misses with a factory chimney, a bridge on the M104 motorway, and a tree, Penelope safely ditches the plane in a field. Parker is thrown clear when the aircraft clips the tree’s canopy and ends up dangling in its branches before dropping to the ground.
Back on Tracy Island, Brains unveils Thunderbird 6 — revealed to be none other than the repaired Tiger Moth — and it’s clear to everyone that this rugged little plane has proven its value in the field.
