John stepped out of emptiness and onto moonlit turf. Reaching up, he opened his visor and took a deep breath of air to try and steady his swimming head. Immediately he wanted to gag, as the stench of petrochemicals and decaying organic matter flooded into him, burning his throat and lungs as it forced its way down into his core. It tasted of death, of a world in the last phases of a terminal infection. And yet, it was also, somehow, alive... Despite its defilement, what he was breathing was the product of plants and microorganisms, not stale chemical factories and endless recycling. Despite the pain that it caused him, he found he could not stop breathing it in.
After some time his body began to adjust, and the air no longer burnt as he gulped it down. With some of his composure regained, he glanced down at the readout on his wrist, and swore under his breath at the figures he saw there. The probability matrix had shifted again and his safety margin was now frighteningly slim. Something had happened while he made the jump - perhaps another rich tourist, too curious for their own good, had got themselves killed in the same crash as Princess Diana - and diffing the checksums between this hell and home would now take almost as much energy as he had left. For a moment he scrolled through pages of commit history, hoping to find a patch to make the calculations faster, but there was nothing - he would have to conserve every last watt he had.
Putting aside the problems of his return, he concentrated on the task in hand. A check with his archaic GPS device confirmed he was in approximately the right position: the last surviving record of a mature European Ash growing in the wild. There were later records still extant, but they were far closer to major population centres and, if he wanted to get home again, coming into contact with other people and their inherent complexities was the last thing he wanted to do. Bit-rot had corrupted the comments associated with the record, but he only had a 100 square metre area to cover. He checked his watch: 00:59. He should have plenty of time to locate the specimen and find cover before dawn.
Looking around, he spotted a rocky overhang - a place where a tree might be able to cling on to life, sheltered from the worst of the elements - and headed off towards it; while beneath him his boots crunched through discarded bottles and crisp-packets. Reaching the overhang, he began to dig through the dune of plastic that had built up against the rock; there were dead things caught buried beneath it and once again he had to fight to stop his gorge from rising.
He had been working for a few minutes when a hint of chlorophyll green caught his eye against the backdrop of sun-bleached waste. Heart surging, he pulled out a half-eaten tarpaulin and the mound of micro-plastics suddenly collapsed, spilling down the slope behind him and revealing a stunted tree beneath. Most of it was blackened and twisted, disease having ravaged the once silver bark, but a single bunch of keys dangled from a stem that looked a little healthier than the rest. Pulling a sample tube from a pocket, he reverently picked the seeds and carefully sealed them away; his hands shaking as if he handled a live bomb. "Thank you," he whispered the prayer under his lips as he rose. "I am sorry we did this to you, but your children will live on."
A hint of movement out of the corner of his eye and he froze. Slowly turning his gaze around, he saw a tiny figure silhouetted against the moonlight, watching him.
"Please don't take them."
The voice was high pitched, and he realised with a start the figure was a child.
"Please don't take them. I would hate to kill you."
He then noticed the glint of moonlight on metal and his limbs felt suddenly deathly cold: the child was armed.
With an effort of will, he tried to keep his voice level. "Take what?"
"The seeds. I need them more than you do".
The child started to walk towards him and, as she stepped from shadow into moonlight, he saw that she was naked except for her underwear and her skin was burnt red by pollution. Fixed to her back, like an engorged metal tick feeding from her, was a device worryingly similar to the one he himself wore.
"What are you?"
"A collector, just like you."
She came alongside him and started to cry when she saw the tree.
"I never thought I would see one."
"A tree?"
She nodded, tears running down her cheeks.
The moonlight had now caught her full on and he could see that she could be no older than twelve or thirteen, barely even a adolescent. But that made no sense: what was a child doing here, half-naked, but wearing the pack of a collector?
Wary of the knife she still held, but aware that she seemed willing to talk, he tried to ask again, "Who are you?"
"I told you, a collector like yourself"
"But there are no children in the service."
"Not in your brane, perhaps; but we are all children in ours".
Brain? The girl's words made no sense, but if she had been alone out here for some time, it would not be surprising if she were a little mad; how had she survived?
"Brain? I'm sorry, I don't follow."
"Yes, brane." Her tone was becoming exasperated; perhaps frustrated at the seeming stupidity of the adult beside her. "You know, brane world, verse, parallel reality. You come back along the pasts of your own world to collect the life that your ancestors destroyed. We come across to yours."
He reeled for a moment at the implications of her words. The energy... "But why could you not do as we do, harvest your own past."
At his words she began to cry again. "We tried, but there were none left. You, I think, come from a grey path; we, from one of the darkest. At each point that your ancestors could have stopped, but only slowed, ours continued. As soon as we discovered how to go back, our pasts were destroyed by the rich travelling to see the world before it ended."
His thoughts flashed back to his arrival here and his anger that someone had jeopardised his mission. The sudden surge of empathy for this strange child who held him at knifepoint almost overwhelmed him.
"But the energy..."
She nodded, gesturing to her pathetic form "Hence why I am a half-starved child. One of the brightest, yes, but still a child. There's less mass this way, less atoms to calculate transformation matrices for. Even then, twenty million people voluntarily spent a year without artificial light so that I could come here."
He nodded to her words, not wanting to understanding them, but nevertheless frightened by the tiny hints of revelation they contained.
"Now I'll ask again. Please don't take the seeds". He detected the steel in her voice and, when he looked at her, was not surprised to see that the knife was again pointing at him. Glancing down at his wrist, he saw that the matrix had shifted again - there was no way now that he was getting home - but this half-starved child might: less atoms to diff that way. For a moment he hesitated - thinking of those he had left behind; then he glanced across at the child next to him and was struck by the desperation that would make her people send her in an adult's stead. When it came down to it, it was a far simpler calculation than the one which had brought him here.
Mind made up, he unsealed the tube of seeds and handed them over to her. He then took off his jump pack and with trembling fingers disengaged the battery.
