[2] Set in 2068, the series depicts a "war of nerves" between Earth and the Mysterons: a race of Martians with the power to create functioning copies of destroyed people or objects and use them to carry out acts of aggression against humanity.
Earth is defended by a military organisation called Spectrum, whose top agent, Captain Scarlet, was killed by the Mysterons and replaced by a reconstruction that subsequently broke free of their control.
"The Inquisition" has been negatively received by commentators, who argue that the clip show device makes for an unsatisfying series finale and criticise the story for leaving the war between Earth and Mars unresolved.
However, his efforts are futile: his overview of the Mysterons' attempt to destroy London ("Big Ben Strikes Again") is judged useless, while his first-person account of the destruction of their base on the Moon ("Crater 101") is rejected due to the extensive coverage that the event received in the news media.
Realising that he has been abducted by Mysteron agents, Blue hurls himself through an observation window and lands on a painted-sky canvas, revealing "Cloudbase" to be nothing more than a replica built inside an empty warehouse.
[12] Colgan was played by a newly made copy of revamp puppet 19, which had appeared in various guest roles in Captain Scarlet and was making its debut as regular character Sam Loover in Joe 90 while "The Inquisition" was being filmed.
[2][10] The episode's original music included a piano piece, performed by series composer Barry Gray, which is heard during the opening scene set inside the Markham Arms.
[9] Anthony Clark of sci-fi-online.com calls it a "cheap flashback episode",[14] while Digital Spy's Morgan Jeffery describes it as a "glorified clip show" that "[provides] no resolution to the series", comparing it negatively to the "thrilling" previous instalment, "Attack on Cloudbase".
He also criticises the story for revealing nothing of Colgan's history and questions the Mysterons' tactics, wondering how and why they went to the trouble of re-creating Cloudbase to interrogate Blue and what they intended to do with the cipher codes had their plan succeeded.
However, he argues that this lack of resolution is more disappointing in Captain Scarlet's case because it was the only series to have "something resembling an overarching story", writing that given this commitment to an ongoing narrative, "The Inquisition" represents an "undeniable anticlimax".
[4] In his review of the CD release of the Captain Scarlet soundtrack, Andrew Pixley of TV Zone magazine names the "sombre" piano piece from "The Inquisition" as one of two standout tracks.