Polly nodded as if she knew what he was talking about, and hoped Nandru would be able to fill her in. While she waited for his input, she sipped from the tin mug Toby handed her, and the memories became more painful than ever before.

Consciousness returned ungently and Tack found he could not move. Staring up at dusty beams, he at first thought the assailant had broken his neck. But it wasn’t the beating that had paralysed him. The familiar sensation of imperatives dissolving in his skull told him that he was connected, as did the raw pain at the back of his neck where his interface plug was located. It was apparent someone had done some home surgery, on this dusty floor he lay upon, to access the plug and connect him up. He was being reprogrammed, and there was nothing he could do about it.

Movement to his left, but he could not turn his head to look. Someone said something in a language he did not recognize, then went on with, ‘Ah, you took your time, but then I suppose that’s to be expected. You AD humans are soft and riddled with imprecise genes.’

The face of the white-skinned man loomed above, his expression contemptuous.

‘You knew the fundamental laws of evolution and you ignored them. You bred strong diseases and weak humans, poisoned with a shitload of inherited idiot programming. You, Tack, have been doubly programmed. And your second program is about to be replaced.’

The stranger liked to talk, that was evident. Tack listened as best he could, through the white noise in his brain, as imperatives were changed and new instructions melded into place.

‘Normally we would have nothing to do with your type, but this opportunity to grow a viable tor we cannot miss.’

The man’s face hovered above Tack again for a moment, then went away. Tack was left with an impression of alienness, but one not easy for him to define.

‘The tor is the device you were sent to retrieve, in a future that does not exist as of here and now. The piece broken off in your wrist, given the right nutrients and conditions, can be encouraged to grow into an entire new tor. And that would be one of which Cowl has no knowledge. Perhaps through you we can get to him at last.’

‘Cowl?’ Tack managed, his voice grating dry in his throat.

‘Ah, Cowl.’ A hiss now came into the man’s tone. ‘Cowl is a step too far for a social species. He is the ultimate individual and, though I hate to admit it, the ultimate application of Darwin’s laws. He kills every threat to him and would destroy humanity to save himself. Your existence is threatened, just as much as mine.’

Tack just didn’t get it—it was all too much. But he did recognize someone far beyond him in the arts of violence, and he wondered about his captor’s programming.

‘You may sit up now.’

Tack did as instructed and found himself on the floor of a barn, in a space walled around with straw bales like huge bricks. Sunlight stabbed through holes in the shiplap wall and illuminated motes of dust in the air. Nearby was an old grey tractor steadily being iced with bird droppings. Tack looked first at his captor, then at the cable snaking from the back of his own neck to a strange-looking portable console propped on some rusting farm implement. The console appeared to have been fashioned from glass, in a suitable shape, then again melted and allowed to distort and sag before cooling. Turning aside, he noticed a ploughshare only inches from his right hand, but he found he could not act on his initial intention, which was to pick up the lump of iron and cleave that white face with it.

‘Pick up the console and stand.’

Tack did precisely as instructed. His programming had changed and he resented it. He suddenly resented all such control: he wanted to be himself. Was this urge part of his new programming?

‘You may detach the cable now.’

Tack obeyed, his fingers pulling the bloody optical plug free from the back of his neck. White-face took cable and console from him and placed them in a backpack. Returning, he reached around and pressed something against the wound in the back of Tack’s neck. Tack could feel the object moving as it occupied the cavity and sealed it shut. The other man then pointed to the backpack.

‘Pick that up and put it on.’

Tack did as instructed.

‘Questions?’

There had never been questions when dealing with his DO. Tack asked anyhow.

‘What do I call you?’

‘You call me Traveller. It is a title in our time, and you do not have my permission to use my given name.’

Tack absorbed our time and wondered just when this man was from.

‘What do you want of me? I didn’t understand you before.’

‘It’s not really you we want, just what is embedded in your wrist.’

Traveller pointed at Tack’s arm. Tack raised it and now saw that his wrist was enclosed in a transparent band filled with esoteric electronics and some sort of gelatinous fluid. Only just could he see the thing embedded in his wrist through all this—it lay at the centre of an array of golden connections almost like an integrated circuit.

‘What’s a tor?’ he finally asked

‘Tors are complex organic time machines: portable and biased towards the past they are sent from. Our machines, unfortunately, must push from the future into that past, against all Cowl’s traps and juggled alternates, and up the probability slope he’s shoving us down.’

‘I still don’t understand.’

‘Of course you don’t. You think linear. What you must be is the ultimate existentialist: only what you perceive is real. If you travel into the past and kill your father before you were conceived, all that happens is you cause an alternate to sprout from that point in time. That act, though, would shove you far down the probability slope, and you would be unlikely to be able to travel ever again. You would become trapped in the alternate you created.’

‘Probability slope?’ Tack felt as if he was trudging through treacle.

‘The parallels are in the form of a wave and the main line sits at the apex of this wave. The other parallels fall down from this apex in descending order of probability. The further down that probability slope you are, the more energy you require to time travel. Both our lines, from our perspective, are coming off the apex. Mine is further down than yours.’

Tack discovered humour. ‘Thank you for clearing that up for me,’ he said.

Traveller hit him and he spun and went down, overbalanced by the pack, blood spurting from his nose into the dirt. Traveller stooped over him, and yanked his head up by the hair. Tack found his hand on the butt of his seeker gun, but he was unable to draw it.

‘When we’re done with you,’ Traveller hissed, ‘I may yet kill you.’ He grabbed Tack’s arm and held it up so that Tack could again see clearly the band around his wrist. ‘Understand that this is all that’s keeping you alive at present, simply because the nutrients it is currently drawing from your body are keeping it alive.’ Traveller then hauled Tack to his feet one-handed, with the ease of a man picking up a rag doll, and shoved him towards the double doors of the barn. ‘Now, get moving.’

The double doors opened onto a yard of compacted road scrapings, along the opposite side of which stood a Dutch barn sheltering a combine harvester, a tractor and the tractor’s various implements. Wiping blood from his face, Tack noticed a plough with its numerous shares polished bright by recent use, and wanted to throw Traveller at this tangle of iron and hear his bones break.

‘Turn to the right,’ said Traveller, and Tack could do nothing but obey his new master. Glancing back, he saw a farmhouse and wondered if it was the same one from which he had heard voices the night before when he had received his beating. Ahead lay a track leading out between fields of newly turned earth, glistening like brown scales in the morning sun. It was cold, his breath steamed in the air, and he noticed frost sugaring the nettles and elder that grew in the shade of the outbuildings.