Master of Worlds (audio story)

 was the fourth and final story in the audio anthology, Cyber-Reality, produced by Big Finish Productions. It was written by Matt Fitton and featured Jemma Redgrave as Kate Stewart, Ingrid Oliver as Petronella Osgood, James Joyce as Josh Carter, Ramon Tikaram as Vikram Shindi, Warren Brown as Sam Bishop and Derek Jacobi as the War Master.

Publisher's summary
The Cybermen are close to victory. A world under Cyber-Control. A new paradigm to expand the Cyber-race.

Fresh from the Time War, arrives at the hour of Earth's greatest need. But he really doesn't care...

Plot
exits his TARDIS and disarms the bomb that Kate was planning to use to destroy Fortress Island. She realises who he is and learns that he came through a door opened by the Cybermen, freeing him from a dimension where he was trapped, and needs replacement components from UNIT for his ship in order to travel elsewhere. The Cyber-Controller breaks in with Osgood, who has had a brainstorm from Cyber-Control across every dimension; she knows who the Master is and has armed herself with a gun lethal to Time Lords. As the Cybermen take them both prisoner, the Master reluctantly appoints himself scientific advisor to help save the world.

Josh saves Kate by taking control of a mobile conversion unit and hits Osgood, who has shot the Master, and the Cybermen with arc lightning. Kate has Josh carry the unconscious Master with them to a helicopter to escape to UNIT HQ and Osgood sends Sam and Shindi after them. As they fly over Battersea, Kate, Josh and the Master see the partially-converted humans assembling units to fully convert themselves and are brought to the roof of the Whitehouse Gallery by the Auctioneers' drones. The Master uses a signal emitter to convert the Auctioneers' soldiers for Josh to test the recharged emotion gun on before killing Julia Hartley-Price with his laser screwdriver.

Kate and Josh force the Master to disarm. Remembering the corrosion virus that the Auctioneers have possession of, Kate realises that it could be of use against the Cybermen and they go in search of it. During the search, the Master steals an egg. Sam, Shindi and the Cybermen track them there after stealing technology from UNIT HQ to do so and the Master breaks their connection to their power source before restoring Sam and Shindi from their virtual conversion using the corrosion virus. Osgood works to restore the disconnected Cybermen and begins to alter a conversion unit to work on the Master and retain his link with his TARDIS.

Kate, Sam, Shindi, Josh and the Master transmat away to UNIT Costermouth using Sontaran technology before knocking out all of the Cybermen on Fortress Island with a field. Shindi and Josh deal with Cybermen flying to the island from the mainland whilst Kate, Sam and the Master go to shut down the dimension bridge, but the Cybermen manage to take down the field. Sea Wolf takes on the Cybermen in a UNIT gunboat as Shindi and Josh go to help the others. Osgood captures the Master and puts him in a conversion unit, but Kate restores her with the corrosion virus and arms the nuclear warhead again. The Master is seemingly partially-converted and, calling himself the Cyber-Master, orders the Cyber-Controller to obey him. The Cybermen submit.

The Master uses the dimension bridge to draw power from realities harmful to the Cybermen. The Cybermen's energy supply is poisoned and harms not only them but also the humans connected to the C-Control. The Master reveals that he was not actually converted and, after taking Osgood hostage for a brief time, returns to his TARDIS and leaves, drawing off the power of the dimension bridge to power it. This has the effect of saving humanity, although Osgood will have to release her patch for C-Control from the Whitehouse Gallery to free everybody. Kate, Osgood, Sam, Shindi and Josh go to save the world.

Cast

 * Kate Stewart - Jemma Redgrave
 * Osgood - Ingrid Oliver
 * - Derek Jacobi
 * Lt Sam Bishop - Warren Brown
 * Colonel Shindi - Ramon Tikaram
 * Josh Carter - James Joyce
 * Cyber-Controller / Cyber-Commander / Cybermen - Nicholas Briggs
 * Julia Hartley-Price - Kerry Fox
 * UNIT sailor - Louis Tamone

Worldbuilding

 * Prior to their first encounter with, the Cybermen of the Cyber-Mainframe are unfamiliar with the Time Lords.
 * The Master is wearing a velvet jacket.
 * Sam compares the War Master's mind tricks to Derren Brown.
 * The Master deduces that Sam once lost a damsel-in-distress.
 * Osgood says that dismantling and cataloguing the artefacts at the Whitehouse Gallery will keep Malcolm busy for months.

Continuity

 * The War Master observes with admiration that the Cybermen are exploiting existing communications technology to control humanity, telling Kate that would be how "[he would] do it." Indeed, in his next incarnation, he will do something similar when he develops the Archangel Network. (TV: The Sound of Drums/Last of the Time Lords)
 * Kate speculates that the War Master had been hiding in the parallel dimension he was trapped in. He quickly avoids the subject. The War Master later flees from the Last Great Time War using a Chameleon Arch. (AUDIO: The Heavenly Paradigm, TV: Utopia)
 * The Master recalls his various battles with the Brigadier and attempts to use hypnosis on Kate. (TV: Terror of the Autons)
 * The Master notes that the Auctioneers' transmat technology is derived from that used by the Sontarans. (AUDIO: The Sontaran Project)
 * The Master suggests that he may one day take over UNIT, which he will do so temporarily when he transforms humanity into the Master Race on Christmas Day 2009. (TV: The End of Time)
 * The Master deduces the military history of Sam's family. (AUDIO: Earthfall)
 * While posing as a converted Cyberman, the Master names himself the "Cyber-Master". In a later incarnation, he will lead a race of Cyber-Warriors converted from Time Lords, whom he names the "CyberMasters". (TV: The Timeless Children)
 * The Cybermen have the ability to fly, which is unfamiliar to Colonel Shindi. (TV: Death in Heaven)
 * The Master laments that he will have to kill Kate another time. Returning with an army of Cybermen, almost succeeded in causing Kate's death if not for the intervention of the cyber-converted Alistair Gordon Lethbridge-Stewart. (TV: Death in Heaven)
 * Osgood is thrilled that she met the Master and survived. Ironically, Osgood, or at least a version of her, was later murdered by Missy. (TV: Death in Heaven)