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 plot of the episode sees Scarlet, Captain Blue and Lieutenant Green set out to destroy a Mysteron installation being built on the far side of the Moon.
The episode is one of four that were later re‑edited and combined to create Revenge of the Mysterons from Mars (1981), a Captain Scarlet compilation film produced by the New York office of distributor ITC Entertainment.
However, unknown to the Spectrum officers, the Mysterons have killed and reconstructed Frazer, a Lunarville 6 colonist who has transported the atomic device to Crater 101 by Lunar Tank.
"[6] Paul Cornell, Martin Day and Keith Topping praise "Crater 101" for its creativity in "[taking] the fight to the Moon", describing it as being among the "finest pieces in the Anderson canon".
He notes that the episode's "discordant" incidental music implies "something ominous" about Frazer and praises the scene of Scarlet "[making] a grab for the crystal" for demonstrating the puppet's mobility.
[9] Andrew Thomas of Dreamwatch magazine considers the sentry vehicles to be an example of the series' occasionally "shoddy" miniature model work, commenting that they "look disturbingly like something out of Michael Bentine's Potty Time.
His review is not without criticisms, calling the resolution involving the CB29 space probe "rather trite" and judging the supporting characters to be poorly written (especially Frazer, who is strangely never seen again after delivering the sabotaged bomb).