A novel of three parts. Two of them are — probably — tightly linked. By some interpretations, anyway. The third — which is the first as presented — brushes up against one of those two, and is to a small extent influenced by it. But in no way that I can discern is it really linked to the others. Which kind of makes me wonder what it’s for.

I mean, sure, maybe he just wanted to tell that story, with no more reason than that. That would be fine. But since the three are presented under one common title, I’ve got to assume that they share more than just a passing brush with simultaneous walks and some sugar in a tank.

The title itself is interesting. The only people who are literally walking on glass at any point are the two exiles from a galactic war in the far future (if that’s really what they are). But glass suggests fragility, slipperiness: maybe everyone is walking on glass, as everything could collapse under them at any moment.

It also suggests transparency: maybe everyone can be seen at any time. If you walk on a sheet of glass, you can be viewed from below. Which sounds not unlike the crosstime telepathic viewing that people in the castle are apparently doing of people in Earth’s past.

All of which leads me to the conclusion — which I didn’t actually expect when I started writing this — that my long-preferred interpretation is the correct one: that Quiss and Ajayi really are former warriors who have been banished to the castle as a punishment for misdeeds. The castle has the technology to let people live vicariously in the minds of humans from its past. At one point Quiss probably touches Grout’s mind and partly causes the road accident.

Is Grout really an exile from the same war, or a similar one? Probably not, but maybe. Maybe someone like Quiss or Aliya touched his mind at some earlier, vulnerable time, and something of their experience passed in to Grout.

But again, what of Graham’s story, and Sara’s betrayal? What does that have to do with the bigger stories?

I remain unsure.