He felt it, the unmistakable sensation of the pestilence. It was impossibly small, but unimaginably intense, like a needle in his eye. It was faint, but pungent, as though the disease had been festering undisturbed in containment for so long that its miasma had built and wafted out, enough for him to taste the scant particles of tainted air.
He had lost track of time in his cell. Doctors had used to come, and bring him specimens to study, to perfect his methods. That had ended long, long ago, when the doctors had realized that they themselves weren't free from disease.
Still, after that, they had still checked on him. The voice would come out of his walls and ask him questions, about what he was doing or how he was feeling, or if he had any regrets for what he'd done.
Regrets.
The thought was as foolish as any he'd ever heard.
Still, even that, too, had faded in time. The voices, long ago, had stopped. And he had been content to rest in this pristine cell, away from the wretched disease, alone with his thoughts. In the constant soft white light that bathed his cell, the doctor reclined himself on a comfortable mattress. Eventually, perhaps, he would have stopped thinking.
But that had been before that familiar, detestable presence had returned, burning at his mind. He found himself standing before the door to his cell, studying it. It had no handle, opened when his captors ordered it.
While the lights had remained functional, the electromagnetic lock had not. His bag contained steel tools, and he did not understand how to relent. It took a tremendous amount of doing, but he got it open a crack, wide enough to put his weight into it. He didn't know how long it took to widen it enough to pass through; he didn't really register the passage of time anymore.
Then, he was in a hallway. Well-lit, and devoid of any other life, all the easier to navigate. He followed the stinging sensation of the disease, navigating the corridors as though he'd drawn up the floorplan. The lights were all functional, all of the other containment chambers still sealed.
At last he found it, behind an unlocked door, within a locked metal locker. His containment cell door had been made of much sterner stuff. In short order the door lay twisted at his feet. He pulled a rectangular metal box from the locker, studying it intently. His finger found a button, pressed it, and the box's lid swung open. Supercooled, preservative gasses mingled with the air outside the box for the first time in a long, long time.
He might as well have been struck in the face. Vapor, colder than ice, wafted in a great cloud from the unsealed box, and he dropped it to the floor with a clatter, which echoed throughout the silent facility. He steeled himself, kneeling down, lifting the face-down box aside, and gingerly plucked the tiny black speck from beneath it with his index finger and thumb. Behind his mask, he grit his teeth, and held the mosquito up to his eye.
It wasn't the insect - it was the sac of blood which the creature had engorged on. The upturned metal box became his operating table, black bag slamming unceremoniously to the ground. His hands dove inside, withdrawing an empty brass syringe, and a vial of thick, black fluid. The needle plunged through the cork stopper, filling the glass cylinder halfway with the viscous pitch.
The needle withdrew, then pierced the engorged mosquito's body, withdrawing the plagued blood within it to mix with the black medicine in his syringe. He left the insect's dry husk on the box, bringing the syringe level with his eyes. He shook it, tapping the glass with his finger to encourage the reaction. He considered the dead husk of the insect still before him. It wouldn't do to let any lingering trace of the pestilence remain in the poor creature.
When he was satisfied with the mixture, the needle found the insect's bloodsac again, filling its tiny body with the cold, black mixture.

The dead insect's body twitched and jerked to life as the black fluid filled it. The body's movement built up a tiny electric charge, enough to reboot the silicon microprocessors in the bug's brain.
Leslie's eyes were the first organ she remembered how to interpret. She… she should be in the living room. That's where she'd gone, but, this wasn't Merle's living room. The blurred figure she saw… it couldn't be Merle.
"Who's there?" she weakly asked at length.
"Hm?" The clarifying black blur shifted, coming more clearly into focus.
"Where is Merle?"
"There is no one here but me, and you." The black form shifted and came closer, until white filled Leslie's vision. She made out the icy grey eyes observing her.
"He… Oh, god, where am I?"
"You are in a prison. Though, the wardens, it seems, have left."
"A prison?" Leslie staggered to stand on her six legs, wings slowly returning to life to beat weakly. "What kind of prison —" her voice cut off as her GPS locator cut on. "Oh god! I'm at Site-19!"
"Is that what this place is called? Odd, after all this time, that I would learn this prison's name from a mosquito."
"I need to get back to Merle!"
"I don't know where, or who, Merle is."
"I know where he lives, I can find it. I just…" the weight of her situation began to dawn on her. She was several hundred miles from Merle's house, in the middle of Site-19, with an anomaly she knew nothing about. Still, at least it wasn't some monster trying to kill her. "I don't know how I could ever get out of here."
The doctor stood up, brought one hand up to curl slowly before his eyes. "I have gotten myself this far, and now that I have, I have no further reason to stay here."
"Then… then you'll help me get out of here?" Leslie's wings bore her up to land on the black-gloved hand.
"I will."
"I can't thank you enough! Thank you! Thank you! I —" Leslie gathered herself, ceasing her trembling. "My name is Leslie. Thank you, um…"
"Doctor."
"Thank you, doctor."

The wind blasted the landscape mercilessly, as it had every day. At least today, there was no astringent rain. Sick, grey-black clouds roiled overhead. The pair had walked for nearly a week, and had not yet encountered a single living person. The few animals they had seen were sick, mangy things.
Leslie felt the sky weigh down on her like a dark grey iron blanket. She was having a hard time remembering what the sun looked like. She was afraid she might start to forget Merle's face. "We're close." she said, to break the monotony. "Just a few more miles, and then… and then…" She didn't dare finish the thought. The sound of the doctor's feet crunching through the parched landscape was barely audible over the rush of wind.
"And then we will arrive." he finished for her.
"Tell me, doctor, why did you come all this way with me? You could have left when we got out, gone your own way."
"Merely because I wanted to."
"Thank you, doctor."

Leslie didn't know what to do when they arrived at Merle's house. The barren streets howled with the wind, but Leslie could only hear the wails of damnation. The lights were off, the door hung open. No one had been here in… in decades.
They went inside. The familiar living room would have made her retch, if she were physically able. Merle wasn't here.
"How long…?" Leslie asked after they had stood in silence in the room where she had died. The question wasn't directed at her companion. She checked the clock on her internal positioning system.
"How long?" he repeated, unsure.
"Two… Two hundred… I've been dead for two hundred years!?" she wailed, collapsing in the palm of the doctor's hands. "Then… then Merle is… is dead."
"So it appears."
"Everyone… everyone is dead." she said, seeming able to grapple finally with the fact. "Everyone…and Merle…and Merle…" she repeated to herself until the words lost meaning to her.
The doctor sat on the frayed, ragged carpet, resting his back against the wall. The hand in which Leslie mourned held out before him. He asked, "Where will you go now?"
"He lived here. He lived here, so now I will live here. It will be just like it was —" she couldn't continue and fell to her side, against the rough but comforting leather. She had no tears, but her sobs wracked her nonetheless. "Any minute… any minute Merle will come through the door."
"Then I will wait for him, here with you."

Going Home

The OCT that spawned it all

Los Días y Las Noches de Leslie y El Doctor

Here you can check out OthellotheCat's take on the pairing.