Unfortunately the base has been beset by some enormous setbacks,especially with their already high pressure assignment. An unusual plague has caused some of Hobeson's team,including the doctor,which causes black veins to appear on their bodies and for them to lose consciousness. Not only that but the Gravitron is experiencing a series of unexpected malfunctions and Hobeson's team are quickly losing control of the device. While himself recovering from his injuries in the bases infirmary with the other plague patients,Jamie observes to Polly and the doctor he has seen a mysterious "phantom piper" as his companions try to help Hobeson deal with the plague.
Dismissing Jamie's claims as delirium, Hobeson and his team are further pressured to repair the Gravitron by Earth despite their confusion. When another member of the team is compromised, Hobeson begins to suspect the doctor and his companions of all the trouble based on the timing of their arrival and that of the malfunctions and,when confronting them on the matter the doctor ushers them away. Shortly after Polly sees what she recognizes as a Cybermen lurking behind the infirmary. When she informs the doctor and Hobeson, he doesn't believe her claims.
Still believing the doctor is somehow involved,he realizes Polly is correct when the doctor deduces when Gravitron operator Evans falls prey to the strange virus during a coffee break. Deducing it came from the sugar used,the doctor takes samples from Evans and finds a Neurotropic virus capable of altering the human nervous system. Meanwhile, the patients of the supposed plague are being taken to a nearby Cyberman vessel and outfitted with devices by which the Cybermen are able to control their movements. Realizing this,the doctor mobilizes the team to find a solution.
Trapped in the infirmary with Ben,Polly suddenly remembers the Cybermen's plastic chest units,and that her nail polish is made of plastic. So she and Ben gather the necessary polymer thinning chemicals from the lab and construct a high octane liquid thinning agent Ben dubs "Polly Cocktail"-with which they disable the invading Cybermen guarding the infirmary so they can assist the doctor and Hobeson further. After a number of failed attempts to keep the Cybermen out,they attempt to extinguish the personnel of the base by breaching it's bio dome with lasers. Unfortunately an Earth rescue ship sent to stop the Cybermen and rescue Hobeson's team are re-directed by the Cybermen controlled Gravitron and sent on a direct course for the sun.
They also manage to regain control of Evans and use him to sabotage the Gravitron and deactivate the security systems-the Cybermen's intent being to use the device to purge the Earth of all biological life. Once Hobeson and teammate Benoit manage to successfully seal one of the Cybermen's breach,the doctor suggests the Gravitron be reversed and set against the lunar surface. When this is done,the Cybermen and their ship are blow off the Lunar surface with their ships. After departing in the TARDIS,the doctor and his companions soon find themselves set upon by the disturbing image of a Crab-like claw. A Macra.
I've seen it written many times that that fourth series of Doctor Who,the first to fully feature Patrick Troughton as the doctor overused the "base under siege" plot line. At the same time this story is an extremely successful one and one of my favorite of the second doctor era. With the visually missing first and third parts brilliantly animated by the same team who did the same for The Reign Of Terror. The idea of a multi cultural human team coming together to use gravitational fields to better stabilize Earth's weather systems is a very captivating one. The possible reality of human politics and need causing this to be a high stress environment adds great drama to the story as well as pointed social commentary.
While there is one very embarrassing effect of two Cybermen flying saucers landing with completely obvious marionette strings attached,not to even mention a few sexist jibes at Polly from Ben Jackson this story actually features some interesting elements. For her part Polly emerges as a strong companion-using know how and science to develop her nail polish like cocktail to disable the Cybermen-as well as assisting as part of the medical staff and still have time to make the coffee. The doctor reveals a possible ability to have an inner dialog with some type of auxiliary brain in his head-a concept not fully explored in the series from this point on. Since it is the only available entry from season 4 of the series thus far,this emerges as a strong and satisfying story all things considered.
