They didn't know how long they fell for; it could have been three seconds or three hours. Scree floated under their fingers and when the pilot tried to switch on his infra-red camera his visor finally gave up the ghost. 6651 wondered if they programmed technology with telepathy so that it would let you down when you most needed it most. Increase in profits would be worth the investment.

Eventually they hit the bottom. Stellada fell and crunching her helmet into the floor. 6651 landed nearby, his impact sending the sound of metal upon metal ringing out. "Stellada?" he called.

"I'm ok," she said. Her voice was weak. The pilot reached out into the dark and found her arm. He crawled towards her, gravel grating on the metal floor.

"Can you see anything? My infra-red's gone and my gun went somewhere when we fell in." She slowly raised her hand to her helmet.

"Yeah, I've got something. I'll turn on my gun torch." Stellada grasped the barrel of her gun and switched it on.

The bottom of the chasm showed what the pilot had been expecting since he saw the opening. Four bodies were not far away from them, a few meters further away from the wall than they were. All four were all impaled on artificial stalagmites rising from the ground. The two of them held their breath as they realised just how lucky they were.

"Shit," Stellada said, disgust in her voice. 6651 pictured in his head a girl that got squeamish at seeing a dead Eros Fish in the Celestrian-Thames.

"Well, now we know what happened to them," 6651 said. He motioned for Stellada to hand him the torch from her gun. He flashed it back up the way they had fallen. "I bet they can't track us down here. Must be something disrupting our transponders. The question is what." It was clearly rock walls and gravel and stone on the floor, but underneath it was definitely metal. And those stalagmites. Things dressed up to look like them, and act like them. He walked over to the bodies and touched the spears of artifice. "These, I'd wager. Someone doesn't want something being discovered. Or didn't, at least. Obviously Greivstorians didn't think anyone would stumble across it by accident."

"There were probably guards as well. And an actual way down, rather than an accident," Stellada said.

6651 shone the torch left and right and found a tunnel on their left. They followed it, Stellada's gun holstered. There didn't seem much need for it anymore.

They walked in silence. The pilot didn't have a countdown on the inside of his visor, but he didn't think it would be more than ten minutes to go. He didn't think he would be back in his Celestrian apartment any time soon, or ever. He had said that the space beneath them would be deep enough and far enough from the focal point of the mushroom to survive it; after all, those at Necrogate were probably going to live through it, but what did he know? He didn't know enough military tactics or history to say whether mushrooming half of a historic city was a good idea, but he doubted it.

The tunnel changed, blending from rock into a lighter shade of grey.

"Artificial rock," the pilot said.

"They built something big down here."

Stellada stopped. She put her hand to her visor.

"What is it? My visor's dead, tell me what you're seeing here."

"It can't be..."

"Don't hold out on me, what is it?" Stellada began to run down the corridor and 6651 chased after her. The ground beneath their feet ran out of gravel and became the mesh of a balcony or walkway, suspended above a large abyss. The walls fell away and a vast expanse opened before them. 6651 could only see the railing at the end, the one that edged a viewing platform for something hidden in the darkness.

"What is it, Stellada?" Moving to a wall, Stellada pushed back a thick tangle of black wires covered in a viscous gloop that smelled like human waste, and pulled a lever.

Large floodlights flickered on. Violet light poured on a cavern so large that they couldn't see the other side On the ground, large egg-like pods sat bubbling away, masses of cables and wires attached to them. The pilot had no doubt what they were. It was the light that did it, that colour.

"Oh fuck," he mouthed. The sight was breathtaking, but of the most terrible nature that he felt sure that his blood would chill and give his heart frostbite.

"Whatever the Greivstorians were using the space for originally, they aren't now," Stellada whispered.

"How many, do you think?" he asked. Stellada looked over at a large bank of monitors and computers along the wall of the veranda. She moved over to one and brought up projections of menus. It was mostly written in a language that was unfamiliar to 6651, but some of the words were obvious. Words like 'bodies' and 'converts'.

"Nearly a billion."

The pilot looked out over the railing of black metal and rubbery flesh. "A billion biomechs waiting to hatch and spawn."