The pad flicked off, and then immediately back on again. He'd had an afterthought. "Oh yeah, I wanted to say ... the things you said to me today -- when I was young -- the encouragement. And the tooth. Well, they meant a lot to me. So, uh ... thanks."

It flicked off.

I put my head in my hands. Everything was throbbing, as if all the universe were contained within an infected tooth. Or maybe the brain tumor of a sick old dinosaur. I'm not stupid. I saw the implications immediately.

The kid -- Philippe -- was my son.

Hawkins was my son.

I hadn't even known I had a son, and now he was dead.

A bleak, blank time later, I set to work drawing time lines in the holographic workspace above my desk. A simple double-loop for Hawkins/Philippe. A rather more complex figure for myself. Then I factored in the TSOs, the waiters, the paleontologists, the musicians, the workmen who built the station in the first place and would salvage its fixtures when we were done with it ... maybe a hundred representative individuals in all.

When I was done, I had a three-dimensional representation of Hilltop Station as a node of intersecting lives in time. It was one hell of a complex figure.

It looked like the Gordian knot.

Then I started crafting a memo back to my younger self. A carbon steel, razor-edged, Damascene sword of a memo. One that would slice Hilltop Station into a thousand spasming paradoxical fragments.

Hire him, fire her, strand a hundred young scientists, all fit and capable of breeding, one million years B.C. Oh, and don't father any children.

It would bring our sponsors down upon us like so many angry hornets. The Unchanging would yank time travel out of human hands -- retroactively. Everything connected to it would be looped out of reality and into the disintegrative medium of quantum uncertainty. Hilltop Station would dissolve into the realm of might-have-been. The research and findings of thousands of dedicated scientists would vanish from human knowing. My son would never have been conceived or born or sent callously to an unnecessary death.