A secret conference to discuss a proposed return mission to Mars is due to be held at Lake Toma, Switzerland. One of the conference delegates, astrophysicist Dr Conrad, will be flying to Geneva Airport accompanied by two bodyguards: Spectrum Captains Scarlet and Blue. The Mysterons have threatened to sabotage the conference. During a pre-flight stay at the Adelphi Hotel, Scarlet and Blue encounter two journalists, Harry and Joe, whose editor is desperate for news stories. Recognising Conrad and sensing a scoop, Harry and Joe follow the Spectrum party to Novena Airport and try to book seats on Flight 104, which will be carrying Conrad, Scarlet and Blue to Geneva. Spectrum has anonymously booked all of the seats to ensure that the trio will be travelling alone. However, Scarlet and Blue ask the airport authorities to admit the journalists to prevent Conrad's movements from being published. Shortly after Flight 104 takes off, its crew are found unconscious in a storage room. It is discovered that they were drugged by Captain Black and that the airliner is under Mysteron control. On Cloudbase, Colonel White orders the launch of the Angel squadron, who intercept Flight 104 over the Alps. Seeing the empty cockpit, the Angels emit warning smoke to alert Scarlet and Blue. After gaining entry to the cockpit by shooting out the door, the officers discover that Flight 104 is nosediving into the Alps. However, the electricity from a power station breaks the Mysterons' hold on the airliner, and Scarlet and Blue are able to pull out of the dive before they crash into a mountain. Flight 104 makes its final approach to Geneva, piloted by Scarlet and Blue. However, one of Blue's bullets has damaged the circuit that operates the landing gear, which fails to deploy. Ordering Blue and the others to the back of the plane, Scarlet makes a successful crash landing but is killed when the front of the plane collides with a bunker. Aware of Scarlet's retro-metabolic powers, Blue assures Harry and Joe that the officer is all right.
Production
The on-screen title, rendered in the series' customary Microgramma typeface, substitutes a letter "I" for the "1". This was done as it was thought that Microgramma "1"s looked too similar to "7"s and that rendering "104" entirely in numerals would be confusing to viewers. The "1"s in the title of the earlier episode "Crater 101" had similarly been replaced with "I"s. The miniature model representing Geneva Airport first appeared as New York Central Airport in the Thunderbirds episode "The Duchess Assignment". The footage of the airport crash tenders moving to intercept Flight 104 was duplicated from "Trapped in the Sky", the first episode of Thunderbirds. The scene in which Flight 104 narrowly avoids crashing into the Alps is accompanied by incidental music that was originally composed for Stingray. The episode also recycles music from Thunderbirds and Supercar. The subplot of the planned return to Mars is continued in the later episode "Noose of Ice", where a new Earth space fleet is being built. Although "Noose of Ice" was originally broadcast after "Flight 104", distributor ITC's official running order places it before this episode, disrupting the continuity.
Reception
Anthony Clark of sci-fi-online.com criticises the pace of the episode, describing "Flight 104" as "torpid".
