"Traitor!" is the sixteenth instalment of Gerry Anderson's Captain Scarlet And The Mysterons. Written by Tony Barwick and directed by Alan Perry, it was first broadcast on 23 April 1968 on ATV Midlands.
In this instalment, following a series of Spectrum hovercraft crashes in the Australian Outback, the Mysterons claim that there is a traitor within the organisation.
The Mysterons declare that there is a traitor within Spectrum. Following a number of unexplained Spectrum hovercraft crashes in the Australian Outback, Colonel White dispatches Captains Scarlet and Blue to the Koala Base training facility, where he suspects that a double agent is sabotaging the fleet.
Scarlet and Blue arrive at the base ostensibly to give a series of lectures to the cadet hovercraft pilots. Base commander Major Stone and cadet leader Joe Johnson suspect Johnson's patrol partner, Phil Machin, of being the traitor; Machin, however, publicly calls Scarlet's loyalty into question after Blue recounts how Scarlet was under Mysteron control when he abducted the World President. A fire in Scarlet and Blue's quarters, apparently started deliberately, leaves Machin's guilt in little doubt.
The next day, as Scarlet and Blue accompany Johnson and Machin on another hovercraft patrol, the vehicle inexplicably malfunctions. Machin openly accuses Scarlet of being the traitor and holds him at gunpoint, but is disarmed when the hovercraft lurches and causes him to drop his weapon. All four men – including Scarlet, who successfully removes the hovercraft's control unit – jump to safety before the hovercraft crashes into a rock formation and explodes.
Analysis of the unit reveals the cause of the accidents, as well as Spectrum's "traitor", to be nothing more than a defective valve in the hovercraft hydraulics. Spectrum metallurgists are baffled by the valve, whose molecular structure seems to have been altered by the Mysterons. The cause of the fire remains unknown.
"Traitor" was shot back-to-back with "Dangerous Rendezvous" on Century 21 Studios' Stage 3.
When Tony Barwick wrote "Dangerous Rendezvous" and "Traitor", filming on Captain Scarlet was several weeks behind schedule. To remedy this, Barwick included a flashback to the series' first episode, "The Mysterons", in each script to reduce the amount of new footage that would need to be filmed; this would enable the two episodes to be shot in 15 days instead of 20. Consequently, Barwick's script for "Traitor" specified that no material from "The Mysterons" was to be included in the series' clip show final episode, "The Inquisition" (which instead contains scenes from "Big Ben Strikes Again", "Crater 101" and "The Trap").
Although the script for "Traitor" allowed for approximately six minutes of recycled footage, the flashback in the finished episode – in which Captain Blue recalls his gunfight with the Mysteron reconstruction of Captain Scarlet and the latter's fall from the London Car-Vu – lasts approximately five minutes. From a narrative point of view, this sequence adds credibility to Machin's suspicions about Scarlet while reminding viewers of the origins of Scarlet's indestructibility.
A number of plot changes were made during the transition from script to screen. The original script makes clear that there is no traitor and that the Mysterons' only involvement in events has been to stir up unrest within Spectrum, that the valve malfunctioned due to the high temperatures in the Outback and that the fire was an accident. A shot of Machin lurking outside Scarlet and Blue's room before the fire breaks out was filmed but later cut so that only a brief sight of a departing figure remains. Cut dialogue indicates that Johnson is Major Stone's nephew, which explains why Stone does not suspect him of being the traitor.
Model-maker Mike Trim based the Spectrum Hovercraft, which appears only in this episode, on his design for the Spectrum Passenger Jet by incorporating a similar forward-swept tail fin. The filming model ran on rubber tyres concealed by its rim and was also equipped with a Jetex motor that created a dust trail to make its movements appear more realistic. Elements of the Koala Base model had previously been used in the episodes "Special Assignment" and "Avalanche".
In the ATV Midlands region, "Traitor" was originally due to air on 12 January 1968 as the 16th episode of Captain Scarlet. The episode did indeed go to air on this date but was interrupted two-and-a-half minutes into transmission due to industrial action. It later aired in full as the 29th episode on 23 April, by which time it had already been seen in the London, Granada and Anglia regions.
James Stansfield of the website Den of Geek ranks "Traitor" the fifth-best instalment of Captain Scarlet, summing it up as a "nice whodunit episode" and commenting that it "does keep you guessing as to who the titular traitor will be". He adds that while the insertion of a flashback to the pilot is "a little unwelcome", the fact that it is narrated by Blue "gives it a nice touch".
Critics Chris Drake and Graeme Bassett praise the design of the Spectrum Hovercraft, describing it as "an impressive addition to the Spectrum fleet" (even though its function within the organisation is not explained).