As she sat eating, and washing down each mouthful with bitter sips from a wineskin, she could hear his woman still angrily moving about outside. He had yelled at her earlier when the woman had protested, whereupon the woman had glared at Polly with both hatred and fear. Polly realized she had to leave now before he came to and wondered what the hell had happened to him. Tossing the duck bone in the fire she reached out for the rest of it, tearing away its stringy flesh with her teeth. The remainder of two flat gritty loaves she shoved into her pockets, then looked around. But there was nothing else here she wanted—no more food anyway. With one last look at the prehistoric man she had sent into a drugged coma, Polly stepped out of the hut. The woman looked up from a quern on which she was grinding some sort of grain. She babbled something Polly did not understand. Polly reckoned her to be not much older than herself, but she appeared terribly worn, like Marjae near the end. Behind her two naked brats were squabbling in the mud. Polly strode past them all to reach the coracle moored on the island shore. The woman shouted a protest as Polly stepped into the small boat and pushed herself away with the paddle. She did not look back.

The sunset was red on the sky when Polly finally moored at another island and crawled ashore. She prepared herself a bed of thick reeds and slumped down on it gratefully. Even as cold as she felt, she was instantly asleep. Night passed in a seeming instant, and as she woke to the dawn chorus of waterfowl and frogs, and then the sound of a man bellowing and threatening. She sat up and he saw her at once and cursed as he waded towards her as fast as he could. There seemed no doubt about what he intended to do with his serrated spear. Polly turned aside, the webwork inside her responsive to the slightest nudge. But there was the suffocation to face.

Try hyperventilating.

‘What?’

Breathe quickly and deeply — more than you need to—until you’re dizzy.

Polly started doing just that. Soon she felt a buzzing through her limbs and became light-headed. As she stepped beyond the bellowing man’s furthest remembered ancestors, the swamp grew thin and it dissipated like fog, exposing a reality of infinite grey over a black sea. Terrible cold gripped her and it seemed as if the pressure of that was aiming to squeeze out her last breath. She was falling now, hurtling through that grey void—the sensation of speed more manifest than before. Briefly she glimpsed a silvery line on some impossible horizon. Surely it must end soon. But as the air bled out of her lungs she began to panic—the scale was going to carry her to the limit again, she was going to run out of breath. Her desperation to stop seemed to distort everything around her into glassy planes, vast curved surfaces, and lines of light. What she needed was down there, and she pulled herself into it. Gasping but elated, she stumbled across frost-hardened ground into the blast of a snowstorm.

Then something growled behind her.

‘Abutment three’ bore the shape of a huge crooked thumb projecting over one corner of the triangular entrance that filled the bottom of this vast chamber. Tack had no wish to look down into the tunnel again, since some effect of perspective seemed to try and pull his eyes out of his head. In the distance he could see a similar abutment overhanging each of the other two corners, and it was a distance—looming through the mist filling the chamber, they stood at least a kilometre apart. Standing back from the edge of the platform mounted on the side of this abutment, and over the rim of which Engineer and various members of his staff were now peering, Tack turned to Saphothere.

‘He told me about the shift back in time, but what was all that about spatial elasticity and the unnecessary squandering of energy?’ he asked.

Saphothere glanced at him. ‘At present the tunnel is one light year long, internally, and a decision must be made as to whether we maintain that physical length or extend it.’

‘But if they are going back a hundred million years, surely the tunnel needs to be extended?’

‘Distance,’ said Saphothere tersely, ‘when equated to time travel through interspace, is only a function of the energy you need to expend. The shorter the tunnel’s actual length, the greater the energy input required to maintain it. Had you sufficient energy you could open a doorway directly into the Precambrian, though you would probably put out the sun in doing it. Zero energy input would extend such a tunnel to infinity, attenuating it into non-existence. It’s quite simple really.’

Tack snorted and returned his attention to Engineer. He and the others had now finished their discussion and rejoined them.

‘It is now decided,’ said Engineer. ‘Take your mantisal through and inform Maxell that we shall maintain the tunnel at one light year. I feel that to extend now would be premature, and that we should wait for the shift into the Triassic’

‘Yes, Engineer,’ replied Saphothere, with a short bow. He turned, and almost immediately their mantisal appeared out of the hot humid air blowing across the platform.

‘And you, Tack,’ continued Engineer, ‘I look forward to seeing again when you return, though you will be much changed.’

Tack did not know what to make of that, so he just nodded and followed Saphothere into the mantisal. Soon they were drifting out from the platform, out over the triangular well below and all its gut-churning distortion. Then the mantisal dropped like a brick, straight down into it.

The falling sensation continued until the mantisal turned, so that rather than dropping downwards as if into a real well, they were now travelling along an immense triangular tunnel. It was only a change of perspective, as the weightless falling sensation continued, but enough for Tack to get a grip on, and so not lose the contents of his stomach. Also, as they progressed, he began to feel acceleration, noticing what appeared to be faults in the silver-grey walls of the tunnel fleeing past faster. All of this was numbing, and just watching it dropped Tack into a weary fugue. He dozed, losing it until Saphothere spoke to him again. Checking his watch, Tack saw that only minutes had passed.

‘Come over here.’

Tack pushed himself away from the side of the mantisal, drifting over to catch hold of a strut, then hauled himself down to a standing position next to Traveller. Saphothere withdrew his left hand from one of the two spheres.

‘Place your hand in there,’ he instructed.

Tack rested his palm against the surface, which felt glassy until he pushed into it, then it gave way and enclosed his hand in cold jelly. Immediately there came a prickling stinging as of numerous needles penetrating his flesh. A chill spread up his arm, across his back, then leapt up via his neck and into his skull. The mantisal suddenly appeared even more transparent than normally, and the tunnel itself changed. Now they were hanging in the flaw of a gem, in which they held their position against a waterfall of light. And beyond this, interspace was again visible—infinite grey underlined by the black roiling of that strange sea.

‘What’s it doing?’

‘Connecting… and feeding as well.’

‘Feeding?’ Tack repeated woodenly.

‘Mantisals draw energy from sources we provide for them within interspace, but that is not enough for a material creature. They separate out carbon from our exhaled breath and, in this manner’—Saphothere nodded towards Tack’s hand—‘directly absorb other essential chemicals.’ Now, do you feel the connection?’

After trying to dismiss from his mind the fact that he was somehow being eaten, Tack did sense something. The mantisal was tired and wanted to rest. It felt confined by the distortion of interspace around it, and was aware of that distortion in a way that—through it—Tack instinctively tried to grasp, but it defeated him. The flow of light now began to diminish, and the mantisal began sliding to the edge of the flaw.