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, James Joyce as Josh Carter, Ramon Tikaram as Vikram Shindi and Warren Brown as Sam Bishop.

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
Cybermen emerge through the dimension bridge and the partially-converted Osgood, Sam and Shindi tell Kate and Josh that they too will be upgraded. Kate and Josh escape and the Cyber-Controller connects Osgood to the Cyber-Mainframe with a cranial upgrade so that she can use her knowledge and the Cybermen's together, her first suggestion being to put off Sam and Shindi's full-conversion.

A UNIT captain leads her soldiers against the Cybermen, but many of them are captured and converted by mobile units. Kate attempts to call for reinforcements without success and instead locks the facility down. She deduces that the Cybermen were using the humans of the other universe as a source of electrical energy and that Josh was immune to the conversion process thanks to his Auton skeleton.

Osgood plans to use the Auctioneers' app to transmit the Cybermen's control signal and make all humans enter conversion units. Her brain goes into overdrive due to her connection to the Cyber-Mainframe but she refuses total conversion and begins her work. The carrier wave containing the signal is blocked, however, as Kate has put up a communications shield before heading with Josh to the armoury to collect weapons to which some Cybermen are known to be vulnerable: a radiation gun, an emotion gun, gold bullets and several grenades. The Cybermen upgrade to become immune to the radiation, but the emotion gun and grenade are effective.

The Cybermen decide to have Kate take down the communications shield per Osgood's suggestion and send the the conversion units to capture her. Kate and Josh barricade themselves into the shielded storage area and Kate cuts her way into a Cyberman with a laser cutter, unwittingly activating a defence mechanism that attempts to convert Josh. Kate stops it by using the laser cutter and removes its helmet, discovering that the Cybermen access their remote power sources using their side handles. She defeats another three Cybermen by throwing a coil over their heads and breaking their connection via electromagnetic interference. Josh struggles with a conversion unit and tells Kate to leave him.

Kate tries to use a coil on the Cyber-Controller, but he has a secondary antenna in his chest unit and she instead damages him up with a grenade. She gases Sam and Shindi and finds that Osgood had reversed the lockdown and disengaged the communications shield. Osgood collapses in pain, but manages to send the new app before passing out. The app is activated and most of humanity is partially-converted through their mobile phones. The repaired Cyber-Controller burns his way into the room where Kate has initiated a nuclear explosion; as the Cybermen get in, a TARDIS that she does not recognise materialises.

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

Worldbuilding

 * The Cybermen have control of 48% of their universe.
 * Kate notes that there are numerous types of Cybermen with subtle differences across this universe and others.
 * Josh notes Jack, Marshall and Neil among the UNIT forces that are most likely dead.
 * Osgood shows the Cyber-Controller her mobile phone.
 * Hearing a TARDIS materialise, Kate initially believes that the Doctor has arrived, but soon realises that the TARDIS in question is not the Doctor's.

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)