General Bron has a new fighter plane, but it is overshadowed by the Red Arrow. He hires the Hood to sabotage the Red Arrow's first flight test, which is scheduled to take place at London Airport under the supervision of Colonel Tim Casey. Sometime later, Red Arrow 1 takes off, but the pilot loses control shortly after take off and the plane crashes into a hangar. Tim Casey is removed from the project.

At the Hood's temple, Bron is pleased but says Red Arrow 2 will be tested soon, and wants it destroyed before he will reward the Hood for his work. At Tracy Island, Jeff and the others pick up an unidentified aircraft approaching, and when they head outside, they see it diving towards them. They think they're about to be attacked, but in reality it's Jeff's old friend Tim Casey dropping by for a visit.

The Hood goes to a relay tower, which has two men called Jim and Stan working inside it. Posing as a maintenance worker, he attaches a device at the bottom of the tower which will effect Red Arrow 2. Back on Tracy Island, Jeff is convinced that the first Red Arrow was sabotaged, something Tim agrees with. Brains creates a diversion detector, which is given to Goddard, who will be the pilot of Red Arrow 2. Goddard leaves Tracy Island and heads to England.

The next day, Red Arrow 2 takes off. However it is soon pulled off course, and Goddard is told to put the plane into a crash dive over open country, then eject. Goddard notices the diversion detector is giving a reading, but he then ejects from the aircraft. Red Arrow 2 ends up smashing into the relay tower, before the two men inside it can get out.

Trapped at the top of the tower, Stan calls International Rescue. With Tim still at the island, just getting the Thunderbirds launched proves to be a challenge, but Jeff gets Tin-Tin to distract Tim whilst Scott, Virgil and Alan head off in Thunderbirds 1 and 2. Tin-Tin takes Tim to an underwater cave, with the promise that a water mamba may be there.

International Rescue arrives at the tower, and see its steelwork is badly damaged. Alan drives a vehicle called the Booster Mortar out of Thunderbird 2's pod, and fires a canister up into the control room. The canister contains two harnesses, which Jim and Stan uses to fly out of the room. Not seen by Scott and the others, they believe they've failed when the control tower crashes to the ground.

However they then see Jim and Stan floating down safely, and realize they've done it. Virgil then notices the device the Hood had attached to the bottom of the tower, which is still functioning. He shows it to Jeff and Brains via video, and Brains says it would explain as to why the Red Arrow was pulled off course. Realizing it really was sabotage, Jeff tells Virgil to warn the police that the saboteur is most likely nearby. Meanwhile, the Hood has driven off, but speeds by a police car. It starts chasing after him, and Bron isn't happy when the Hood tells him that International Rescue must have found evidence and have involved the police. The Hood smashes through a police diversion and claims to have lost them.

However the diversion was actually there to warn people the bridge ahead was out, and the Hood drives right over it. He crashes his van, and whilst he survives, the radio is still working. Bron calls him a fool who can't even drive a car, and tells him to fend for himself now. Back at the island, Tin-Tin's distraction tactic has worked, and she is given a signal that things are clear again. She and Tim then go back.

When Tim gets back to the lounge, Jeff tells him about what's happened with the Red Arrow, and that he has been reinstated on the project. Goddard returns to pick Tim up, and as they leave via jet, Tim has another message for Jeff deployed.

Notes

-During the opening, the plane is shown attacking a boat. The shot of the boat exploding was taken from Star of the East, an episode of Stingray.

-The Red Arrow plane is probably named after the real-life aerobatic team known as the Red Arrows.

-The interior of the control tower at London Airport looks completely different to what it looked like in Trapped in the Sky and Operation Crash-Dive. It makes less sense if viewing in the broadcast order, as this episode aired between those two.

-When Norman is talking about clearing the area, a number of aircraft can be seen. Most prominently is the TX 204 seen from Trapped in the Sky, along with a repainted WASP Spearhead bomber from Stingray.

-When Red Arrow 1 crashes into the hangar, two more WASP bombers can be seen in the hangars next to it.

-A few shots in this episode have been taken from Trapped in the Sky, including the emergency services heading out when Red Arrow 1 is about to crash, and Goddard parachuting after ejecting from Red Arrow 2.

-When Brains and Alan find out about the approaching aircraft, Braman from Sun Probe can be seen behind them.

-Jeff mentions about the visitor perhaps being another of Tin-Tin's admirers. This is a reference to Eddie from End of the Road, although if viewing the series in the broadcast order it wouldn't make much sense since that episode aired after this one.

-The relay tower is owned by British Telecommunications. This episode first aired in 1965, around 15 years before the real British Telecommunications (now known as BT) existed.

-There is a hint there was a scene deleted from the episode. At one point, Alan asks Virgil if he's ok, despite nothing happening. You can then see a pile of debris on the ground near Virgil. It suggests to me Virgil was meant to nearly get hit by some falling debris, but this got cut.

Errors

-Why is the American air force testing a new plane at a British public airport? And whilst the newspaper Jeff reads states Casey will be replaced, Norman ends up having to run the second test flight himself.
-When the Hood parks his van, there are two cars in nearby spaces. These cars swap positions when the Hood drives off.
-Scott refers to Tim as a General instead of a Colonel at one point.
-When Scott gets up after Casey's pretend attack, part of a puppeteer's hand can briefly be seen at the bottom left.
-The little Virgil figure doesn't have a coat on during the Booster Mortar scene, but he is wearing one for the puppet shots.