Treble Cross

Plot

Major Gravener, a test pilot for the World Air Force, was en route to Slaton Airbase in a car driven by his chauffeur, Harris. From the opposite direction, Captain Black drove a truck and used a beam fitted with false headlamps to blind Harris. To prevent a crash, Harris swerved the car into a lake, and both he and Gravener drowned. Two passing doctors found Gravener, who was clinically dead, and took him to Slaton Hospital.

There, a stasis and recovery unit revived him. The following day, a Mysteron reconstruction of Gravener went to Slaton Airbase and seized an XK-107 bomber carrying a nuclear warhead. When news of Gravener’s accident reached the base, personnel recognized the pilot as an impostor and blocked the runway just as he was taking off. The XK-107 crashed and exploded, killing the reconstructed Gravener.

Spectrum linked the attempted theft to a Mysteron threat to destroy Futura City, the world capital. After being briefed by Captains Scarlet and Blue, the real Gravener took off in a second XK-107 to deceive the Mysterons into believing he was their duplicate. As expected, Captain Black contacted the aircraft and ordered Gravener to land at the disused Weston Airstrip, thirty miles outside Futura City. Scarlet deduced that the plan was to transfer the warhead to a ground vehicle; Gravener would then fly the XK-107 as a decoy while the warhead was driven into Futura City and detonated.

Black’s truck was seen waiting at the airstrip. As Gravener came in to land, Spectrum ground forces in a Patrol Car, led by Scarlet and Blue, converged to capture Black. The truck tried to escape but swerved out of Gravener’s path and crashed into a bunker. To their shock, Scarlet, Blue, and Gravener found the dead driver was not Black but a Mysteron reconstruction of Harris.

Blue concluded that while the Mysterons could not tell the two Graveners apart, Black had a sixth sense that warned him of danger, allowing him to evade Spectrum once more.

Production

"Treble Cross" is a Captain Scarlet episode written by Tony Barwick, one of several of his scripts that reference July 10. Barwick would often include this date because it was his birthday, and fans now celebrate July 10 as "Captain Scarlet Day". The episode took two weeks to film in September 1967, and during that time Century 21 was starting pre-production on their next Supermarionation series, Joe 90. The miniature model used for Slaton Hospital had earlier appeared as a laboratory in the episode "Place of Angels". To make Major Gravener's revival more convincing, the puppet was given a bag inside its torso that could be pumped with air, making the chest rise and fall. The footage of Spectrum forces gathering at Weston Airstrip was originally shot for "Manhunt", another episode where Spectrum tries to capture Captain Black.

Reception

Anthony Clark of sci-fi-online.com found the episode's setup more engaging than that of "Fire at Rig 15," though he felt the pacing dragged a bit. Shane M. Dallmann of Video Watchdog magazine described it as "less amusing but far more intelligent" than "Flight to Atlantica." Fred McNamara offered strong praise, highlighting the episode's "confident, propulsive" storytelling and its "disarmingly simple" approach. He noted that while "Treble Cross" pushes the series beyond its usual territory, it stays grounded with "plenty of mystery, intrigue and action."

McNamara particularly enjoyed watching the Mysterons lose ground as Spectrum takes charge. However, he had some criticisms: the crash of the XK-107 should destroy its nuclear warhead, but the on-screen explosion is too "fairly compact" to make that clear; the reveal that the reconstructed Harris is the truck driver felt anticlimactic; and the episode never explores the revived Gravener's potential "crisis of personality" after being duplicated. McNamara observed that the story doesn't allow time for Gravener to reflect on having his body used by the Mysterons and, to some extent, by Spectrum.

Media historian Nicholas J. Cull identified "Treble Cross" as one of several Captain Scarlet episodes showcasing writer Tony Barwick's recurring concern with nuclear technology. Cull saw the plot—an attempted theft of a nuclear warhead—as Barwick revisiting one of his favorite plot devices.