‘Best get to the trees as quickly as we can,’ said Traveller. ‘Out here we’re likely to get stomped.’

Tack saw that the man was tired again and his eyes lifeless. Traveller gestured to a distant elephantine shape coming towards them.

‘Mammoth,’ Tack said.

Traveller snorted. ‘Wrong. They’re ten million years in the future. That thing over there is a deinotherium—a rather larger and more bad-tempered ancestor of the elephant. So let’s move.’

They dropped out of the mantisal and walked away from it. Glancing back, Tack saw the strange thing fold out of existence, leaving a cold mist that swiftly dissipated. Nearby he saw huge skins of excrement covering the ground, some old enough for plants to be pushing up through them, and some new enough to be covered by legions of flies contesting ownership with dung beetles the size of golf balls. Avoiding these, they tramped on towards the trees, keeping a wary eye on the approaching beast.

‘How big is it? I can’t really tell,’ Tack asked.

‘About four metres high at the shoulder. We could bring it down with our weapons, but even this far back in time every drastic action we take creates difficulties for the mantisal.’ Seeing Tack’s puzzled expression Traveller went on, ‘We come from the potential future, and no matter how careful we may be our actions here affect that future.’ He gestured all about them. ‘Our presence here is even now moving this time-line down the probability slope, leaving as the main line all this without our presence. Therefore, in each jump through time we make, the mantisal takes us not only back in time but back up the slope to mainline time. And the more we influence each time we are in, thus affecting our probable future, the more slope it has to carry us back up on the next jump. Luckily, the further back we go, the less we affect our probable future.’

Reflecting on their previous conversations, Tack said, ‘I’d have thought the danger would increase the further back we went.’

His expression showing his customary irritation, Traveller glanced across at him. ‘Which shows just how little you understand. As I said before: kill your father before your conception and you’ll end up right down the slope, where it would take the full energy output of the sun tap for a whole day to propel you back onto the main line. But to achieve the same screw-up here, you’d need heavy weapons—and as far back as, say, the Jurassic, nothing less than a tactical nuke.’

‘I don’t understand.’

‘No, of course not.’ Traveller said nothing more for a while then, relenting, added, ‘Errors like that do not accumulate through time. There’s an effect called temporal inertia. By travelling back in time and killing your father, you push yourself down the slope because of the paradox you’ve created. Kill your direct ancestor a hundred million years in the past, and you’ll still be born.’

‘But doesn’t that mean… predestination… some controlling intelligence?’

‘Only in the way that a tree is predestined to grow towards the sun, and only in the way that some god might have made that tree. Evolutionary forces are macroscale as well as microscale.’

‘But—’

‘Enough. Just think about what I’ve already told you. It is doubtful you’ll be able to understand it all anyway. You still think linear.’ Just then the deinotherium let out a roar and was suddenly charging towards them, kicking up a cloud of dust.

‘It is probably in must,’ said Traveller. ‘Pick up your pace.’

Tack did so readily, glancing back the way they had come as he broke into a trot. ‘Perhaps that’s pissed it off,’ he commented.

Traveller looked back, too, and his expression changed. The mantisal had returned, hovering just where they had previously abandoned it. Tack now did a double-take—it clearly wasn’t their mantisal, since it contained four individuals who were even now scrambling out of it.

‘Umbrathane,’ Traveller hissed. ‘Run!’

The order was reinforced through Tack’s programming, so without conscious volition he found himself obeying. As he ran he drew his seeker gun, and he wondered if he had received some subliminal instruction to do that as well. A triple flash to his side: Traveller was firing with that weapon of his, then sprinting past Tack to turn and fire again. Suddenly the grass to their right was burning and the air full of smoke. Again the deinotherium roared, and now they could feel the thunder of its progress.

‘Shed the pack!’

Still running, Tack obeyed, regretting the loss of the equipment it contained. But regret was dispelled when Traveller came sprinting past him with the same pack slung from one shoulder, as if its weight was of no consequence. Tack glanced back and saw the four newcomers heading directly towards them. Then the elephantine mass of the enraged animal thundered in between, drawing a veil of dust between them and their pursuers.

‘Move faster!’

From somewhere inside himself, Tack found his last few ergs of energy and accelerated. But no matter how fast he ran, or dodged from side to side, Traveller was in front of him, behind him, to the side, crouching and firing, then up again and sprinting away. Traveller was fast, more so than any human Tack knew of, and the man made Tack feel slow and clumsy, which he had never felt before.

Behind them, the deinotherium’s aggressive roaring changed to a panicked trumpeting, and Tack glimpsed back to see it turning aside, smoke boiling off its hindquarters, as black-clad figures moved quickly past it. Suddenly a tree exploded to Tack’s left, and it was only then that he realized they had finally reached the forest. Loud detonations and flashes continued to move off to his left—the direction Traveller had veered in as they entered the trees. Tack just kept running as hard as he could. In fact he could not stop, and knew that if Traveller did not cancel his last instruction soon, he, Tack, would die of a ruptured heart.

Stop.

The order at last came through Tack’s comlink as he was running, in the agony of lactic overload, down a black tunnel of trees. He immediately sprawled forwards on the ground, his muscles locking with cramps and his lungs feeling torn as he gasped for breath. Distantly he could still hear the trumpeting animal.

Hold your position and, excepting myself, kill anyone who comes to you.

It was some minutes before Tack could even pull himself to his knees. His seeker gun was clasped tightly in a hand as white as tooth enamel, and it took him a severe effort of will to unclench his fingers and drop the weapon. For a while he tried to massage the agonizing cramps from his legs, then taking up his gun again he dragged himself to cover amongst dense ferns beneath a fallen forest giant, partially supported off the ground by its own massive side branches. There he lay still and listened to the deinotherium’s cries of outrage fading away.

After a hiatus, the birds started singing. He found nothing in their song to comfort him as he lay with his jaw still clenched rigid, while he tried to rub the agonizing knots from his legs. Slowly the pain was dispersing, but it would be some minutes before he would be able to get about on them again. As yet no suspicious sound or sign of movement.

Then the birdsong suddenly stopped again, and the most glorious face Tack had ever seen gazed down at him—before a hand like a nest of steel bars grasped the back of his collar and hauled him out of hiding.

The watcher, mind and body in glass, had tracked the course of the tor over brief centuries from this particular vorpal sensor, finally turning it out from interspace to track her progress in the real world. Upon seeing the girl thrashing her way through the woods and talking to herself, it was not difficult to surmise that this was one torbearer who would not survive long. But the omniscient voyeurism was almost addictive, and there had been something odd about those insane monologues… After a brief exchange with the girl, the wagon driver, presumably the Amazing Berthold advertised, jumped nimbly down to the ground and swept off his hat. And the watcher decided to listen in.