I don't own Doctor Who.
We will Survive.
Cybermen and their conflicts with humanity always made the Doctor think, and as the TARDIS left Pete's World - there was just enough Artron energy to allow the TARDIS to break through the dimensional barriers and return to N-space; this was a difficult manoeuvre at the best of times, but with the limited resources at his disposal, the Doctor needed complete silence and concentration. Indeed, when Rose had begun speaking to him about Mickey being left behind, even begging and whining that they couldn't leave him without once taking into account Mickey had made his choice, the Doctor had immediately hypnotised her to force her to sleep so he could work; it was a temporary measure, and Rose would not remember a thing.
While he regretted resorting to using that method, the Doctor couldn't concentrate on the tricky coordinates and speaking to Rose at the same time. For a long time, the Doctor concentrated on carefully focusing the TARDIS through the dimensional barriers.
The moment the TARDIS returned to her home reality, the console began glowing more brightly, indicating that the TARDIS was using its copy of the Eye of Harmony to siphon off energy from the Time Vortex itself to replenish whatever energy had been lost during the fall into Pete's World. The Doctor grinned at the sight of his beautiful ship returning to life; when he had seen the burnt-out console and the steam rising from the walls of the ship, he had been hearts broken by the sight of his oldest friend dead.
There had been many occasions over the centuries where he had been terrified the TARDIS was gone; the old girl had come close once or twice.
The time where the Fluid Links had exploded before he and Jamie had met Zoe, the time the TARDIS had landed on Frontios where she was scattered over the surface of the planet as her control systems were shaken up by the time jump into the far future over the Gallifreyan Noosphere when the TARDIS took in the Faction biodata virus and then imploded after his eighth self had blasted Gallifrey with what was left of her power systems where she was then forced to regenerate herself for a hundred years, the fight with the Ravenous in the final years of his eighth incarnation which had drained her of so much power.
The Doctor gasped as he remembered, the crack in time.
After setting up the Relative Dimensional Barriers to close the crack, and heal whatever damage there was while also making sure the TARDIS siphoned off whatever residual energy would be created by the two realities interacting with one another, the Doctor stepped back and thought about the latest - unwanted - adventure, and he felt like shuddering.
He had been to parallel universes many times in his lives, although not deliberately; the first time he had slipped into a different true alternate universe was in the early days of his third incarnation when his experiments to repair the TARDIS and resume his travels after the Time Lords exiled him to Earth (the Doctor tried not to think about the possibility the Dictator in that reality was his counterpart, but he knew thanks to the Brigadier, a version of the Master was there and had been tortured by the Republic of Britain following an encounter with the alternate Great Intelligence), but the parallel universes created by the Monk in his seventh incarnation, and the realities he had experienced during his eighth incarnation who'd been forced to travel with his memory completely gone following the battle against Grandfather Paradox and compressing his mind to make room for the Matrix of Gallifrey to save the Time Lords from completely being destroyed had helped him with his experiences with parallel universes.
The Doctor knew he could blame Mickey all he wanted for his own mistakes, but he wasn't going to now he was gone. Nobody was to blame for the TARDIS falling through the vortex into that parallel universe, although he would need to find a way to make the TARDIS warn him of other cracks in the Time Vortex.
Pete's World was parallel to its N-Space counterpart, and the Doctor knew if Earth of this reality developed their technology ever so slightly, it wouldn't be too different from what he, Rose, and Mickey had just seen. Well, and also made use of zeppelins, but what scared the Doctor the most was the discovery of Lumic's experiments.
He had already been concerned and worried about the ear pods after seeing the public stop and accept the latest download of news of all kinds into their brains - that type of technology was quite invasive and there were so many ways somebody could take advantage of the technology and cause incredible levels of damage, but the Doctor knew there wouldn't be anything he could do about it with his meagre resources. With the TARDIS out of commission, and his uncertainty if UNIT existed although even if it did, they wouldn't know him, and he was in no position to demand they do something about Cybus Industries.
But that hadn't stopped him.
While he had let Rose see her delusions about her parallel parents, which was probably a big mistake now he was thinking about it in hindsight, (what she was thinking of, the Doctor didn't know, but it had been worrying since there was the chance she would ditch her Jackie to live with the Pete World versions of her parents; it wouldn't work out, of course, but Rose was too stubborn to listen to him and she'd needed to experience the truth for herself), the Doctor had been checking a computer linked to Cybus, and he had watched as pitch described the creation of a new race of Cybermen.
The Cybermen were his deadliest enemies, right beneath the Daleks and the Master, although the Doctor knew he would never meet his Time Lord enemy again, sadly enough. But while they were deadly, even the Doctor could understand and see ways the Cybermen's bionic and cybernetic implants could do so much good, and he could understand Lumic's desire to live, but how many times had he seen different races repeat the same mistakes of Doctorman Allan and the Committee who had merely converted the entirety of Mondas's population after his visit with Nyssa back in his fifth incarnation; all he had done was merely delay the inevitable after defeating the Committee.
Lumic had merely made the same mistakes as Mondas had, but at the same time, he had acted in much the same way as Davros had, and created something powerful and discovered the power in it, believing it to be superior to what was there before. The Cyber-Lumic had boasted he had created an everlasting peace, but all he had done was create a production line.
But he had seen the Cybermen grow many, many times before, and now it appeared he would do so again. While he despised the Daleks especially now they'd fought in the Time War, there was just something about the Cybermen and their cold, brutally logical approach to surviving at all costs while they conquered worlds and transformed humans into Cybermen like themselves. One of the worst invasions the Doctor would always recall was his eighth self's travels with Destrii and how the Cybermen had journeyed back in time and tried to convert humanity. All they wanted was to survive; Lumic had been no different and he had imbued the same desire into his creations, so despite their different origins and slightly different technology, the Cybus Cybermen had been the same as their N-Space counterparts.
Coldly logical beings driven to survive at all costs who'd cut out the one thing which separated them from machines all to stop themselves going insane when the conversion process removed their brains and placed them inside the cybernetic shells.