Earthfall (audio story)

 was the second story in the audio anthology, Extinction, produced by Big Finish Productions. It was written by Andrew Smith and featured Jemma Redgrave as Kate Stewart, Ingrid Oliver as Petronella Osgood, James Joyce as Josh Carter, Tracy Wiles as Jacqui McGee and introduced Warren Brown as Sam Bishop.

Publisher's summary
Lieutenant Sam Bishop is finishing an assignment in Bangkok when he receives a call from Kate Stewart. She has a new job for him — hunt for a stray Nestene energy unit that has come down somewhere in the Gobi desert.

In Mongolia, Sam is joined by Osgood and they set off into the Gobi. But there are Autons in this desert. They are also looking for the energy unit, and they're ready to kill anyone who comes into contact with it.

Back in London, Kate is becoming suspicious of Simon Devlin's company, and decides to pay him a visit.

Plot
In Bangkok, Sam finds a woman who has been infected and mutated by an alien crystal and uses a stun net to capture her after she becomes hostile. After ordering UNIT to lock the crystal away and transport the woman to Group 6 in Tokyo, he receives a call from Kate telling him to travel to Mongolia to recover a Nestene energy unit which fell to the Gobi Desert after hitting a satellite. Instead of sending Osgood to Africa to assist the tracking teams there, Kate sends her to join Sam.

The Nestene Consciousness is concerned about the lost energy unit and tells Devlin that, if UNIT reach it first, their plans must be accelerated. Devlin, however, has already made arrangements for its recovery.

Osgood and Sam head to Dalanzadgad and are debriefed by Kate using a hologram projector. Josh informs Kate that a discreetly-purchased subsidiary of Devlin Futuretech has increased its purchase of crude oil by over 500% in the last year and it seems likely that Devlin is working with the Nestenes. Kate visits him and asks about his disappearance last year, learning that he suffered from fibrous dysplasia and has had his skull replaced with a plastic one. He reveals that he knows about UNIT and warns her not to interfere with his business given his connections.

Osgood and Sam find the crater, but the energy unit is missing and, after knocking Sam out, Jenna Gold and her Autons kidnap Osgood. Sam is found by Tarkhan and taken to his camp where he hands over the energy unit. Removed from its metal box, it is detected by the Nestenes and Tarkhan prepares to fight them. Devlin sends Jenna to find it and cuts across her before she can ask about Osgood's claims that the Autons are alien, having been told that they were built by Devlin Futuretech.

After leaving Devlin, Kate and Josh are followed by Jacqui and learn from her that people who have tried taking their printers apart have been found dead. Sam contacts her and she appears in the Gobi Desert as a hologram, checking on Osgood and telling her to run from Jenna before Tarkhan's tribe begins their attack on the Autons. Sam is wounded in the fight and, to keep the Autons from falling into the hands of the authorities, Devlin orders them to kill Jenna and then themselves. A new wave of energy units begins to fall and Kate sends Sam to Puerto Rico.

Osgood brings the energy unit back to the United Kingdom and Sam reports from the Arecibo Observatory that more than two-hundred units are on their way. Kate tells him to keep her posted and updates Geneva, needing their permission to move in on Devlin. Josh, however, has already made plans to infiltrate Devlin Futuretech.

With the energy units soon landing in remote areas where they can easily be recovered by Autons, the Nestene Consciousness tells Devlin that Earth will soon be theirs.

Cast

 * Kate Stewart - Jemma Redgrave
 * Osgood - Ingrid Oliver
 * Lieutenant Sam Bishop - Warren Brown
 * Captain Josh Carter - James Joyce
 * Tarkhan - Ramon Tikaram
 * Simon Devlin - Steve John Shepherd
 * Jenna Gold - Karina Fernandez
 * Jacqui McGee - Tracy Wiles
 * The Nestene Consciousness - Nicholas Briggs

Continuity

 * Sam is aware of the Nestenes' relationship with UNIT. (TV: Spearhead from Space, Terror of the Autons)
 * Kate gets nervous when sitting in a plastic chair. (TV: Terror of the Autons)