S4E25
Gritty yet hopeful
Written by Kit Pedler
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The Moonbase Part 3

When the Cybermen invade a moonbase with a plan to destroy Earth by controlling the weather, the Doctor and his companions must find a way to stop them before they succeed in wiping out all life on the planet.

The Doctor, along with his companions Polly, Ben, and Jamie, arrive at a moonbase only to discover it under attack by the Cybermen. These cybernetic beings, thought to have been defeated, are revealed to have infiltrated the base with a sinister plan: to use the Gravitron, a powerful weather-controlling device, to devastate Earth. Led by Commander Hobson, the moonbase crew struggles to understand the Cybermen's motives and find a way to resist their technologically superior force.

The Cybermen begin converting the base's human personnel into Cybermen, expanding their ranks and control. The Doctor learns that the Cybermen have bypassed the base's defenses by contaminating the food supply to enter without detection. While Hobson and the remaining crew try to maintain control of the base, the Doctor works to understand the Cybermen's plan and their weaknesses. Ben and Polly discover that a plastic component in the Cybermen's chest units is vulnerable to certain solvents.

As the Cybermen prepare to activate the Gravitron and unleash their destructive weather patterns on Earth, Polly and Ben concoct a solvent mixture aimed at dissolving the vulnerable chest units. They arm themselves with makeshift spray devices and, along with Jamie, confront the Cybermen in a climactic showdown. The solvent successfully destroys the Cybermen. The Doctor realizes that the sonic fields created by the gravitron can disrupt the converted humans. Using this knowledge, he disrupts the Cybermen's control of them, freeing their minds and stopping the device.

With the immediate threat neutralized, the Doctor and his companions discover that the Cybermen's main ship is about to invade. In a desperate move, Ben uses a fire extinguisher refilled with the solvent mix to attack a Cyberman outside the base. The crew then repurposes the Gravitron's coil lenses to target the Cybermen's ship, hoping to disable it before it can launch an attack on Earth. Facing an imminent threat and internal sabotage, the Doctor and his friends work together to defend humanity from total destruction.


Events in This Episode

The narrative beats that drive the story

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Act 1

The Cybermen initiate a brutal invasion of the moonbase, commencing with a swift assault on the sickbay. They ruthlessly kill Bob, an unarmed crewman, and assert immediate control over Commander Hobson and the Doctor. Their mechanical voices and cold demeanor underscore their alien and emotionless nature. Cyberman 1 explicitly states their objective: to seize the Gravitron, a powerful weather-controlling device, and unleash destructive atmospheric changes upon Earth, thereby eliminating all life, which they perceive as "dangers." They reveal their cunning infiltration method, having bypassed the base's defenses by cutting a hole beneath the surface and contaminating the food supply, explaining the previously observed air pressure drops. While Hobson and Benoit grapple with the shock and the Cybermen's chilling lack of mercy, the Doctor begins his subtle observations, noting the Cybermen's reliance on converted human personnel. Concurrently, confined in the sickbay, Polly and Ben initiate their own investigation into potential weaknesses, recalling past encounters with Cybermen and speculating about the composition of their chest units, identifying a plastic component as a possible vulnerability. This act effectively establishes the overwhelming threat, the Cybermen's ruthless agenda, and the nascent efforts of the protagonists to understand and counter their technologically superior foe, setting a desperate tone for the struggle ahead.

Act 2

This act details the development and execution of the moonbase crew's desperate counter-strategy against the Cybermen. Confined to the sickbay, Polly, inspired by Jamie's comment about "sprinkling witches," conducts a crucial experiment, successfully demonstrating that acetone can dissolve plastic. This breakthrough leads her and Ben to meticulously concoct a potent "Polly cocktail"—a mixture of benzene, ether, alcohol, acetone, and epoxy-propane—designed to attack the Cybermen's vulnerable chest units. Simultaneously, in the control room, the Doctor, through careful observation, deduces that the Cybermen are using converted humans as tools because there's something in the Gravitron's operational environment they dislike. He subtly manipulates the R/T unit, causing the converted men to lose coordination, confirming his theory that the Cybermen control them via sonic fields. As the Cybermen prepare to align the Gravitron's field rectors to devastate Earth, Ben repurposes fire extinguishers into makeshift spray devices, arming himself, Polly, and Jamie with the solvent. The act climaxes in a daring assault on the control room. The trio bursts in, spraying the Cybermen's chest units, which instantly bubble and dissolve, causing the Cybermen to collapse. They then quickly remove the metal helmets from the converted men, freeing them from control and temporarily neutralizing the immediate threat posed by the Cybermen within the base.

Act 3

The narrative immediately pivots from the internal victory to a heightened external threat, as the Cyberleader, having lost contact with the defeated ground forces, orders a full-scale invasion by the main Cyberman ship. This escalation forces the moonbase crew into a defensive posture. Commander Hobson dispatches Benoit to investigate the missing surface party, leading to a critical discovery: Cybermen weapons are rendered inoperable in the vacuum of space. This newfound vulnerability is quickly exploited when Ben, demonstrating remarkable ingenuity and bravery, dons a spacesuit and confronts an attacking Cyberman on the lunar surface. He effectively uses a solvent-filled fire extinguisher to destroy the Cyberman's chest unit, showcasing the continued efficacy of their improvised weapon even in extreme conditions. Back inside, Hobson takes decisive action, rallying the remaining personnel to lower armored doors, secure all exits, and task Charlie with re-establishing vital communication with Earth. The Doctor, ever the strategist, collaborates with Hobson, inquiring about the Gravitron's structural capabilities. Learning that its main coil lenses can be repositioned, he begins to formulate a desperate plan to repurpose the powerful weather-controlling device into a defensive weapon, aiming to target and disable the incoming Cyberman ship before it can launch its devastating assault on Earth. This act sets the stage for a final, high-stakes confrontation, transforming a tactical victory into a strategic struggle for survival against a larger, imminent threat.