Code Silver (audio story)

 was the third story in the audio anthology, Cyber-Reality, produced by Big Finish Productions. It was written by Guy Adams and featured Jemma Redgrave as Kate Stewart and Ingrid Oliver as Petronella Osgood.

Publisher's summary
The Cybermen are coming. Across the barriers between universes, conquering all before them. Conquering and converting.

As her troops fight a relentless enemy, Kate battles to lock down the threat. But how long can UNIT resist?

Plot
Inside the laboratory on Fortress Island, Josh Carter observes that several figures are marching through the dimension gate towards him and Kate Stewart. The two fire their guns at the figures to stop them, to no avail; several Cybermen emerge from the dimension gate, with one proclaiming that Kate and Josh's weapons are "insufficient". The partially-converted Shindi, Sam Bishop and Osgood state that Kate and Josh will be upgraded. Kate and Josh quickly exit the laboratory, before Kate broadcasts a Code Silver alert across Fortress Island. The duo then head to Kate's office, despite Josh's reluctance to not wait for reinforcements.

Back inside the laboratory, a Cyber-Controller exits the dimension gate before ordering Osgood to stabilise the dimension bridge and activate a signalling shield. Osgood does both, before stating the names and professions of herself, Shindi and Sam to the Cyber-Controller. Realising that Osgood's scientific knowledge will be useful, the Cyber-Controller forces Osgood to undergo a cranial upgrade, much to Osgood's discomfort. Now connected to the Cyber-Mainframe, Osgood marvels at the sheer amount of knowledge and ideas that she has access to. The Cyber-Controller states that Shindi and Sam will be fully converted, but Osgood orders him to wait until full seeding of Earth has commenced. Despite its initial doubts, the Cyber-Controller checks Osgood's brain pattern and realises that her response is logical, not emotional. Osgood states that, having observed the dimension seeding protocols, they can be improved, explaining that she can guarantee greater results in a shorter timeframe, so long as Shindi and Sam are not fully converted yet, and she has a short amount of time to work. The Cyber-Controller agrees to Osgood's proposal, before ordering the other Cybermen to take full control of the island with the assistance of several mobile conversion units.

Several UNIT soldiers take their positions near the laboratory and fire when several Cybermen exit; the Cybermen immediately massacre the soldiers in response. Meanwhile, Kate and Josh reach Kate's office, observing the battle via the security cameras. Kate discovers that the Cybermen are blocking communications from the fort, preventing her from calling for backup. Josh notes that the conversions of Osgood, Sam and Shindi are similar to the conversions of the lifeforms he encountered with Osgood and Shindi on the parallel Earth they visited. Kate hopes that their conversions can be reversed, and theorises that as the virtual reality headsets were broadcasting carrier waves, they must be able to transmit matter. She then quickly locks down the entire fort, stating that their mission was never evacuation; UNIT must stop the Cybermen spreading across Earth with whatever means necessary.

Returning to the security cameras, Josh observes with surprise the arrival of several giant, metal spider-like machines; one grabs a soldier, and seconds later, a Cyberman exits the spider's conversion chamber. Kate realises that the "spiders" are mobile conversion units, enabling the Cybermen to upgrade people on the fly. Observing the laboratory's security camera, the duo realise that Osgood is working on something, and begin quickly analysing what they already know: Osgood, Sam and Shindi are under mind control with limited physical conversion, potentially allowing Kate and Josh to restore their humanity if they can figure out how the mind control works and either block or reverse it. Josh and Kate further analyse that the VR headsets took Josh, Osgood and Shindi to a parallel Earth under complete Cyber-control, despite the absence of any Cybermen; Kate reasons that the Cybermen conquered the planet and moved on, possibly leaving a small force behind. The humans stored in the pods underneath Piccadilly Circus were awaiting full cyber-conversion, and the Machine stated that "the flesh was useful" and gave "energy". Kate questions if the Machine was referring to electricity, noting that human bodies generate small amounts of electricity; an entire Earth of human batteries would be a viable power source. She then reasons that this is the Cybermen's main invasion tactic; occupy a planet, turn it into a power source that the Cybermen can tap into, and move on, repeating the process across the universe. The "dimension seeding" that the Machine referred to is exactly what the Cybermen are currently doing - as well as expanding in their home universe, the Cybermen are using the VR headsets to form bridgeheads into parallel universes. Josh questions why the VR headsets' control signal failed to work on him; Kate concludes that, as the signal was calibrated to human biology, Josh's Auton skeleton was enough to scramble it. Commenting that theorising under pressure is the "story of her life", Kate tells Josh to follow her to the communications room.

Back in the laboratory, Osgood analyses the dimension seeding protocols, commenting that it is simple but slow. The Cyber-Controller argues that it is effective at achieving Cyber-control of a planet in an acceptable timeframe, but Osgood critiques that the human authorities have many opportunities to stop the Cybermen. Osgood calls the Cyber-Controller's thinking arrogant, to which the Controller states that, having conquered 48% of their home universe, the Cybermen will conquer the rest within 7849 years; therefore, the Cybermen are unstoppable. In response to Osgood's surprise, the Controller simply states that "the universe is large", before telling Osgood that her emotional responses are delaying the completion of her work. Osgood simply continues, confirming that the Cybermen use mind-controlled lifeforms as part of the dimension seeding protocols because they recognise the value of a lifeforms's local knowledge when attempting to convert a planet - knowledge that is lost upon full conversion. The Cyber-Controller begrudgingly confirms this. As Osgood marvels at what she can now do with her connection to the Cyber-Mainframe, the Cyber-Controller claims that Cyber-Technology is the most advanced technology in the multiverse, despite what Osgood calls its single-minded function: conquer a planet, move on, rinse and repeat. She jokes that speeding up the Cybermen's methods is not a good idea, as the Cybermen will be highly bored when they have converted all of reality.

Osgood then states that the key to her strategy is the dimension bridge technology - the VR headsets. She states that the Cybermen can transfer the headsets and basic upgrade components to other universes, but cannot transfer themselves before establishing a signal in the new universe. The Cyber-Controller states that the dimension bridge technology has been translocated to many universes, awaiting use to open the way for the Cybermen's expansion. Osgood further states that the headsets transmit a control signal containing mind control and basic upgrade components; the Cyber-Controller states that Osgood can already see all of this information through the Cyber-Mainframe, but Osgood asks the Controller to talk her through it for her plan. The Cyber-Controller states that once the headsets have been used to establish a link between universes, basic upgrades follow; Osgood confirms that, although the process takes extensive time to complete if there is a dimensional gap between the user and the signal, the process can be instantaneous if the mind of the user and the signal are in the same dimension. From this, Osgood states that she can bring Earth under total Cyber-control in a matter of minutes.

To be continued

Cast

 * Kate Stewart - Jemma Redgrave
 * Osgood - Ingrid Oliver
 * Josh Carter - James Joyce
 * Lt Sam Bishop - Warren Brown
 * Colonel Shindi - Ramon Tikaram
 * Cyber-Controller / Cyber-Commander / Cybermen - Nicholas Briggs
 * UNIT Captain / Soldier - Katherine Jakeways

Continuity

 * Osgood tells the Cyber-Controller that UNIT's Black Archive would dispute claims of the Cybermen being unstoppable. (TV: The Invasion et al.)
 * Kate suggests that Josh's Auton physiology made him immune to the VR headsets' control signal. (AUDIO: Bridgehead, Armageddon)
 * Kate is aware of at least two separate origin points for the Cybermen: one in N-Space (TV: The Tenth Planet et al.) and one in a parallel universe (TV: Rise of the Cybermen / The Age of Steel) which attempted a invasion of N-Space. (TV: Army of Ghosts, Doomsday)
 * Kate speaks of the parallel evolution of the various Cyberman races. (TV: The Doctor Falls)
 * Osgood recalls the app created by the Auctioneers. (AUDIO: Game Theory)
 * Kate notes that UNIT has a stock of gold bullets for use against Cybermen. (TV: Battlefield)
 * Kate mentions that depending on the variant of Cybermen they are facing they are susceptible to radiation (TV: The Tenth Planet), Acetone (TV: The Moonbase) gold, (TV: Revenge of the Cybermen, Silver Nemesis) and emotion. (TV: The Invasion)