A Fireflash aircraft crashes, with the loss of all hands - not least because the position given by the flight crew is considerably inaccurate. The entire fleet is grounded, but repeated tests fail to identify the cause of the accident. Determined to track the problem, a test flight is made, and an identical problem occurs. This time, International Rescue are on the scene and cut the massive engines away from the craft, allowing it to rise to the surface.
Continued, thorough tests fail to locate the problem, and International Rescue are called to assist. With the highly-trained Scott Tracy as co-pilot and with Thunderbird 2 flying alongside, a second test flight is made. The same critical failures occur, but this time Gordon Tracy is able to enter Fireflash's wing compartment and attempt repairs. There, he discovers the terrifying truth about the Fireflash crashes...
- A Day in the Limelight: Thunderbird 5 has a much bigger role in this episode than usual, since it is used to keep track of the Fireflash test flights.
- A Million is a Statistic: This episode has a pretty high body count when you consider the first Fireflash (with hunderds of unseen people on board) goes down without IR around to help. IR does go out of its way to save the two pilots aboard the second one.
- Combat Pragmatist: Gordon tricks the saboteur into trying to parachute out of the Fireflash, then shoots him in the back.
- Continuity Nod: The episode constantly references the series premiere, Trapped in the Sky. Several characters from that episode return.
- Take a Third Option: In the climax the third Fireflash, with Scott and Gordon on board, is about to crash into the ocean, and Gordon realizes there is no time to properly fix the cut cable of the Elevator Power Unit. His solution; just hold the two ends together with his bare hands. It works.
- Up to Eleven: Thunderbird 2, the biggest Thunderbird, is utterly dwarfed next to the Fireflash.
- The Unfavorite: This episode makes it pretty clear Gerry Anderson didn't like John. Thunderbird 5 for once gets to do something other than relay the mission of the week, and this Day in the Limelight for the space station coincides with Alan being on duty relieving John.
- Vehicular Sabotage: What happens to several Flashflash crafts.
- What the Hell, Hero?: Not only does International Rescue not launch to save the first Fireflash, they don't even bother to radio the search and resuce teams to let them know they're looking in the wrong place.