CHAPTER TWO

Following in the Doctor's wake, Rory struggled to climb up the shifting dune, feeling the soft sand seeping insidiously into his shoes. The sensation made him shudder. He wasn't quite sure what entropy dust was, but the tone of the Doctor's voice had made it plain that it was nothing good. He couldn't shake the eerie feeling that he was walking over one big grave.

Things only got worse when he reached the top of the dune. Amy and the Doctor were looking out over a huge, bowl-like indentation in the ground, their faces horror-struck. For a moment, Rory thought he was gazing at some sort of strange lake, the silver surface heaving in a continuous, oddly unpleasant rhythm. But then he realised it was not liquid at all, but a vast, solid mass of insectile creatures, millions of them, walking over and under and around each other, teeming in endless, perpetual motion, each of them struggling upward to reach the light, only to be forced back down by a myriad of other creatures equally determined to end up on top.

"Well, that explains a lot," the Doctor said, his eyes darkened with disgust.

"Wh...what are they?" Amy gasped. "There are so many of them! Are they...alive?"

"In a manner of speaking," the Time Lord replied. "They're SRMs."

"SRMs?" Rory repeated, unable to take his gaze off the repulsive creatures crawling beneath them, his eyes unwillingly drawn in sick fascination to the undulating tangle of spindly legs.

"Self Replicating Machines," the Doctor explained. "Invented in the 51st century by Frederick Kreitzer, an engineer working for the Gaia Corporation on Earth. They were supposed to be the perfect tool for colonisation of sterile planets. All the Gaia Corporation had to do was to drop one SRM on to the surface of a planet and then sit back and watch. That initial SRM would then begin to absorb matter from its surroundings and convert it, using it to replicate itself almost instantly. From there, the process would continue and before long there would be four of them, then eight, and so on and so forth. Once they reached the optimum workforce number, they were programmed to stop replicating and begin terraforming the planet, commencing construction of cities and other vital infrastructure. In theory, the Gaia Corporation would end up with a brand new luxury settlement, just waiting for high-paying human colonists to move into – a very profitable venture indeed."

"You said 'in theory'? What happened?" Amy queried tensely.

The Doctors mouth tightened. "There was a problem with the code that never showed up in the developmental simulations. As it turned out, once released on the surface of a planet, the SRMs didn't pause to build a city. Instead they just kept on reproducing, continued eating up the planet to make copies of themselves, until there was nothing left. In the end, production and use of SRMs was deemed too risky and they were universally banned by the Shadow Proclamation."

"But they're here, on this planet!" Amy exclaimed. "The beautiful rainforest you told us about..."

"All gone," the Doctor ground out, his voice taut with anger. "Like so many other irreplaceable things, thanks to human greed."

Rory stared at the frenzied, pointless activity below. He couldn't help thinking how much the swarming creatures resembled horrible, long-legged silver spiders. Suddenly, with a thrill of horror, he realised the activity was no longer quite so pointless. Thousands of pairs of tiny, silver antennae were now waving in their direction, the apparently random movements of the SRMs coalescing and becoming more purposeful.

"Doctor..." he said warningly, his throat suddenly dry. He could see a wave building beneath them, swelling the rolling, grey surface. The SRMs were working together, standing on each other's backs, in a concerted, intelligent attempt to reach the three time-travellers watching from above.

"Uh-oh, not good," the Doctor breathed. "They've sensed the arrival of new raw materials, just waiting to be broken down and converted into new SRMs."

"What new raw materials?" Amy demanded, instinctively backing away as the seething tower of slender, silver limbs rose closer and closer.

"US!" the Doctor yelled. "RUN!"