A 2021 Dalek civil war, known to the Time Lords as the Security Drone Incident, (PROSE: Dalek Combat Training Manual) was fought on Earth in January between the race of Daleks imperfectly cloned by an ancient Dalek recon scout and the Death Squad Daleks. The latter had been summoned to Earth by the Thirteenth Doctor in a gambit to curtail the cloned Daleks' attempted takeover of Earth. (TV: Revolution of the Daleks)
A day to come
Through the extrapolations of the Matrix, the Time War-era Time Lords foresaw this event from the Doctor's personal future, which was recorded in the Dalek Combat Training Manual. They were aware that Big Bang Two had caused subtle changes to the timeline of Earth, resulting in events such as the earlier 21st century Dalek invasion being forgotten, such that humanity at large would be unfamiliar with the Daleks as was evidenced in this incident.
It came much to the concern of the Time Lords that a single Dalek was able to create a whole new mutant strain of the Dalek race without the advanced skills of Davros, the Dalek Emperor or the Cult of Skaro. As such, they began research into the genetic make-up of the Reconnaissance Daleks to further understand the extent of their abilities. (PROSE: Dalek Combat Training Manual)
During the Recon Scout Incident (PROSE: Dalek Combat Training Manual) of January 1, 2019, a Dalek reconnaissance scout that had been defeated centuries prior in the Battle of Hope Valley was inadvertently revived after one of its pieces was rediscovered. The Dalek attempted to resume its mission, but came up against the Thirteenth Doctor and her "extended fam", who melted its casing and ejected the Dalek mutant into a supernova, destroying it. (TV: Resolution)
The destroyed Recon Scout's casing was recovered and, having been tipped off by Jo Patterson, stolen by Jack Robertson. Robertson employed scientist Leo Rugazzi to replicate the alien technology to create Defence Drones in order to protect Great Britain. Leo discovered fragments of the Dalek's DNA and cloned the creature, unaware of what it truly was and effectively resurrected the Dalek because the clone possessed the consciousness of the original as "Dalek consciousness can live within the tiniest fragment of the their DNA." The Dalek linked into the systems of Robertson's company and secretly created a clone farm in Osaka, Japan to create an army of thousands of new Daleks, albeit ones with corrupted DNA due to the human origin of the clones. (TV: Revolution of the Daleks)
In January 2021, (WC: The Defence Drones) new Prime Minister Jo Patterson unveiled her plan to use her new Defence Drones to protect the country from threats. Team TARDIS, who recognized the Daleks from defeating the original Recon Scout, attempted to stop Robertson without the help of the missing Thirteenth Doctor, without success. As the crisis escalated, the Doctor returned after having been broken out of prison by Captain Jack Harkness. The Doctor, Ryan Sinclair and Graham O'Brien confronted Robertson, while Jack and Yasmin Khan investigated the clone farm and attempted to destroy it.
Robertson showed the Doctor and her companions that the Defence Drones were just AI-controlled shells, but the Dalek took control of Leo when he attempted to destroy it. At the clone farm, the Dalek revealed its plan to exterminate humanity and use Earth as a base to conquer the universe. Via ultraviolet light, the Dalek mutants teleported into their casings and began exterminating humanity across England, killing numerous people including Patterson. Before teleporting into his casing, the Dalek scout killed Leo. (TV: Revolution of the Daleks)
With thousands of Daleks marauding across the United Kingdom, the Doctor realized that the only option left was to summon more Daleks to Earth in order to deal with the army intent on exterminating humanity. The Doctor used the TARDIS to broadcast the Reconnaissance Scout signal into the Time Vortex, where it was quickly picked up by a Dalek saucer full of Death Squad Daleks.
Responding to the signal, the Death Squad Daleks detected the Defence Drone Daleks on Earth and dispatched thousands of troops to exterminate the other Daleks due to their impure DNA. On a bridge in Bristol, squads from both sides converged and, although the Defence Drones insisted that they had only mutated in order to survive, the Death Squad Daleks saw them as inferior beings that needed to be exterminated. Although the Defence Drones attempted to defend themselves, they were no match for the more advanced Death Squad Daleks and were quickly exterminated. Witnessing the intelligence and might of the Death Squad Daleks, Robertson betrayed humanity and offered information if taken before their leader. The Death Squad Daleks were victorious over their man-made counterparts and, within a short period of time, exterminated them all. (TV: Revolution of the Daleks)
Destruction of the Death Squad
As Death Squad finished exterminating the Defence Drones, the Doctor enlisted Jack, Ryan and Graham to board the Dalek saucer and destroy it in order to get rid of the winning faction in order to prevent them from conquering the Earth. Teleporting to the ship using Jack's vortex manipulator, the three men spread out to plant explosives supplied by Jack around the vessel. However, Jack witnessed Robertson reveal to the Dalek leader that the Doctor had sent the signal that brought the Daleks to Earth and that it was a trap. As Robertson attempted to negotiate an alliance with the Daleks, the clone of the Recon Scout teleported aboard and attempted to convince them to spare him. Seeing the Dalek as impure, the Death Squad Daleks refused and exterminated the clone as they believed that it was the only method of purification.
As Ryan and Graham joined him, Jack informed the Doctor that the Defence Drones had all been wiped out, but warned her that Robertson had informed the Daleks of her presence on Earth. Knowing that destroying the Dalek ship wouldn't be enough to stop the other Death Squad Daleks, the Doctor ordered Jack to hold off on detonation until he received the signal from Yaz and laid a trap using her spare TARDIS. Changing the outer appearance of the TARDIS to match hers using the chameleon circuit, the Doctor flew it into the skies of Earth and used a holographic projection to trick all of the Daleks into flying inside.
On the Dalek ship, Jack, Ryan and Graham reluctantly rescued Robertson, but they were detected by the Daleks and cornered and faced extermination. With the other Daleks in the TARDIS, Yaz gave Jack the signal and he teleported the group out. As they teleported out, Ryan detonated the explosives that he, Jack and Graham had placed throughout the Dalek saucer, destroying the ship and all of the Daleks still onboard. In the TARDIS, the Doctor's holographic projection revealed her trick and that she had programed the TARDIS to fold in on itself and teleport into the heart of the Void which would destroy the remaining Death Squad Daleks. After promising that she would outrun the Daleks every time, the Doctor cut off communication with them as the TARDIS imploded and teleported into the Void, destroying the last of the Daleks on Earth. (TV: Revolution of the Daleks)
In the aftermath, Robertson defended his betrayal as being a decoy to save the Earth and, with no one on Earth the wiser to his true actions, he was hailed as the "saviour of the world" and faced a possible honorary knighthood and another chance at becoming the President of the United States. (TV: Revolution of the Daleks)