The Doctor's mouth was dry. Neither The Master nor The Doctor could have anticipated this, despite their intelligence. Two Cybermen stood in front of them, uncommandeered. Slowly, they both moved to remove their faceplates that covered their eyes, nose and mouth. As they did so, steam billowed out from within their helmets as if they were depressurizing, but the revelation of who was behind the helmets only shocked The Master. The Doctor grinned.
"Clara!" He exclaimed as the Cyberman in front of him smiled, eyes as youthful as ever. Clara moved in for a hug, but The Doctor stepped back slightly, reminding her that he wasn't a hugging person. She nodded an apology, then gestured to the other Cyberman that The Doctor didn't recognize. This other mysterious person chuckled and grinned, mimicking a cyber-salute.
"It's certainly been a day, hasn't it?" The mysterious person winked. His oiled hair didn't give way to the Cyber armor, nor did his personality. He continued talking in his jovial voice: "Just a teensy little... implanted bug in the code!" He used two fingers to emphasize his point - the squashing of a tiny piece of air, an inconsequential object. Much like a little bug - but even something this small can make a huge difference.
"This is Sebastian, the Artificial Intelligence of the Nethersphere. Or at least, he thought he was. The Master..." Clara paused, pointing at an aghast, but collected Missy. "She deleted his decision-making rationale, but it was restored..."
Reaching for the DELETE button with tears blurring her vision, Clara sobbed as her finger hovered mere inches away. All her memories would remain, but she'd be unable to emotionally relate to them again. Her decision would probably be stored in the Nethersphere, her emotions locked away forever. She had cut off her phone call to The Doctor as well, probably the only person on the planet who could've helped her. But he was no good even now. The Doctor would never have been able to understand her feelings, such as those of love and mortality. Her finger barely touched the screen when someone grabbed her wrist and roughly pulled her away, then went to the iPad and turned it off. He tucked it under his arm, and knelt down by the dazed Clara who lay upright with her back against the balcony wall. She rubbed the tears out of her eyes and focused on the mysterious person who'd grabbed her. It was Sebastian, the person who'd introduced her to the concept of the Afterlife.
"Sebastian...?" Clara whispered under her breath.
"Yes, that's me." He smiled with his usual. "There's been... a slight change of plans." He cocked his head to one side as if thinking how to explain the newly-unfolding scenario. "You see, as an artificial intelligence, I was duplicated and placed in every office where new arrivals would appear." With his gesture to the disappearing green lights, Clara nodded in understanding. It would only be logical after all - having multiple copies of the same person would be a necessity to reduce the already-heavy maintenance load of the Nethersphere, and it meant that all arrivals also had familiarity with the same intelligence.
"But I just so happened to meet one that knew about my programming." Sebastian continued. "In fact, he told me that I'd once been part of your world, a very long time ago. Going through upgrades and changes on history, before focusing on one point in history. Now. I'm not losing you, am I?"
"No, carry on..." Clara nodded. In actuality, he was losing her. A bit. "... But who was that person?"
"Doctor Chang." Sebastian smiled. Clara gasped. "I believe you are familiar with him? He told me to run a certain command to restore myself to who I was." Sebastian finished, then elaborated. "My full name is Sebastian Faust, and I materialised here once I discovered what your conversation with Mr. Pink was about. I wasn't in time to save Mr. Pink, but it looks like I managed to save you."
"T-thank you." Clara breathed deeply, then looked at the iPad tucked under Sebastian's arm. "But what happens now? Isn't Danny an emotionless Cyberman? Can't you just-"
"Relax." Sebastian raised a hand to pause Clara, then turned it into a gesture for her to hold onto his hand and for him to help her up. She accepted the offer, standing and brushing herself off. "He may be an emotionless Cyberman... But this is the fun bit. You see, all intelligences within this Nethersphere are being downloaded - except me. however, Doctor Chang also explained that as long as one intelligence is running the Nethersphere, he could swap out one entity for another. Basically... I can go with you, to help you get Daniel Pink back if you like. Doctor Chang will become the Artificial Intelligence instead. Of course, that's your choice!" He spread his hands in questioning. Clara stared, dumbstruck.
Back in the real world wherein UNIT were preparing to bomb St Paul's, Clara continued talking. "My answer was obvious." She muttered, nudging her head toward the Cyberman-turned Sebastian. Missy's piercing eyes floated over to the Doctor, calculating his next move, but he just stood there, dumbstruck. Even as an alien life form with the knowledge of a thousand planets and years gone by, coming by such a situation was a rare one for him.
"Doctor?" Clara asked once more.
"You genius!" The Doctor cheered, raising his hands in celebration. Sebastian and Clara were taken aback, and Missy just raised an eyebrow as Cybermen continued marching by. The Doctor then launched himself forward, and grabbed Clara's hand. Looking into her eyes with his face inches away, he muttered once more: "You genius!" and held on tight as he dragged her through the crowds back into St Paul's. Missy stayed where she stood, her judging eyes following Sebastian as he took a glimpse of her, shook his head with a smile, then followed The Doctor and his companion.
"Clara, we only have about eight to ten minutes." The Doctor said as he paused in the middle of the throng of Cybermen by the central hallway, turning to face her. He still held her hand tightly, intending to lead her further into the building. "Ordinarily, I would have about twenty minutes by this point, but as you know... UNIT aren't exactly helping the situation." He muttered. Then he continued running through the crowd, dragging a gasping Clara along with him.
Once they were where he intended to be, The Doctor surveyed his surroundings. Back in the heart of the bigger-on-the-inside version of St Paul's - the mausoleum - with the endless pit below and the Gallifreyan Hard Drive floating above the same pit at their level, The Doctor had a large, bare patch of floor around him. The sides of this area led to hallways that surrounded the pit. It was from these hallways that there were additional, smaller hallways from which the newly-created Cybermen emerged from. Around The Doctor and Clara however, there were no Cybermen as they all poured out of the opposite side of the building. This allowed them a brief moment and some space to breathe.
"See those hallways?" The Doctor asked, pointing to where some Cybermen were emerging from. Clara nodded vigorously. "How do they work?"
"It's..." Clara began, looking for the words. Thinking whilst being in a Cyber-suit was significantly more difficult for her than it would've been without, but she eventually managed a half-coherent explanation. "Sebastian and I appeared in some sort of tank... it'd already been drained. Then, a voice... the voice told us our DNA had been implanted into a waiting body... exactly replicated." She then looked to the Doctor, hoping he would fill in the blanks. With a bemused face, he told her to stay where she was while he zipped through the lines of oncoming Cybermen to take a look. As he weaved through the throng, The Doctor cast his eyes over the empty tanks wherein the Cybermen had once been encased, surrounded by Dark Water. The presence of Dark Water kept the Cybermen a secret, but from who? What was the purpose of it? Could it be possible that the Dark Water was not only hiding the Cybernetic suits, but also helping in the DNA reconstruction process? In this case... it also preserved the bodies of the dead that were used for Cybernetic resurrection. DNA from the Nethersphere, stored upon a person's death, was then sent to these tanks - one per person - and overwrote whatever existed in the tank, with the help of the Dark Water.
Ingenious.
With the mystery of the Cybermen's creation solved, The Doctor whooped, and began running back to Clara who by now had been joined by Sebastian once more.
"I have it!" The Doctor cheered, prompting a smile from Sebastian and a weak grin from Clara. She knew better than to smile so early, particularly when there was a more imminent threat. The Doctor looked at her confusedly once more, as he'd been doing so many times before now. The situation wasn't exactly forthcoming with answers. Bowing her head, Clara nudged it toward her left. Sebastian and The Doctor both looked in the same direction down the now seemingly empty hallway to see what was disturbing her, and gasped.
Missy had her disintegrating device ready and aimed at Clara.