• • •

On the Lady Mac 's bridge, Marcus said: «We originally assumed that the xenocs would just go into zero-tau and wait for a rescue ship; because that's what we would do. But their technology allows them to take a much different approach to engineering problems.»

«The wormhole leads into the future,» Roman said in astonishment.

«Almost. It doesn't lead anywhere but back to itself, so the length inside it represents time not space. As long as the portal exists you can travel through it. The xenocs went in just after they built the dish and came out again when their rescue ship arrived. That's why they built the portal to survive so long, it had to carry them through a great deal of time.»

«How does that help you get here?» Katherine asked. «You're trapped over in the xenoc wreckage right now, not in the past.»

«The wormhole exists as long as the portal does. It's an open tube to every second of that entire period of existence, you're not restricted which way you travel through it.»

• • •

In the portal chamber Marcus approached one of the curving black buttress legs. The artificial gravity was off directly underneath the doughnut so the xenocs could rise into it. But they had been intent on travelling into the future.

He started to climb the buttress. The first section was the steepest; he had to clamp his hands behind it, and haul himself up. Not easy in that gravity field. It gradually curved over, flattening out at the top, leaving him standing above the doughnut. He balanced there precariously, very aware of the potentially lethal fall down onto the floor.

The doughnut didn't look any different from this position, a glowing ring surrounding the grey pressure membrane. Marcus put one foot over the edge of the exotic matter, and jumped.

He fell clean through the pressure membrane. There was no gravity field in the wormhole, although every movement suddenly became very sluggish. To his waving limbs it felt as if he was immersed in some kind of fluid, though his sensor block reported a perfect vacuum.

The wormhole wall was insubstantial, difficult to see in the meagre backscatter of light from the pressure membrane. Five narrow lines of yellow light materialized, spaced equidistantly around the wall. They stretched from the rim of the pressure membrane up to a vanishing point some indefinable distance away.

Nothing else happened. Marcus drifted until he reached the wall, which his hand adhered to as though the entire surface was one giant stikpad. He crawled his way back to the pressure membrane. When he stuck his hand through, there was no resistance. He pushed his head out.

There was no visible difference to the chamber outside. He datavised his communication block to search for a signal. It told him there was only the band from one of the relay blocks in the stairwells. No time had passed.

He withdrew back into the wormhole. Surely the xenocs hadn't expected to crawl along the entire length? In any case, the other end would be thirteen thousand years ago. Marcus retrieved the xenoc activation code from his neural nanonics, and datavised it.