And maybe it is because of this small non-exchange that I realise what is special about Caleb. The woman with the buggy made an attempt at human interaction but when she saw the look on Caleb’s face, she faltered. Not because he was rude or hostile – his expression was a blank – but because in that instant it became obvious to her that she had failed to read him. It was only a tiny moment – she will have forgotten it by the time she has pressed the button to call the lift – but it has made me realise that I, too, have failed to read Caleb. I have been watching him with more intensity than I have lavished on any of the many other human beings I have been observing, and yet his thoughts remain a mystery to me.

I think about this for a while and the more I think about it the more true and obvious it feels. Most of the time, I know what people are thinking, or can at least make a guess. It’s not that I can read their minds – hundreds of people pass through this station every day, just imagine the clamour if I could. But when I look at PC Lockhart, I know what is troubling him. When I see Tom, it’s obvious to me that he is thinking with some degree of envy about Inspector Barker’s new ukulele and wondering when he’s going to get a look at it. Melissa is so bright, so ambitious, her face radiates it. I know for a fact she is thinking about applying for Area Management and worrying that it will mean a lot of time away from home and how that will be for her mum. And Dalmar, Dalmar is suffused with a quality possessed only by people who have suffered and survived long enough to put their suffering aside: an overwhelming sadness coupled with an ability to keep on, day by day. Dalmar has seen some terrible things done to human beings by other human beings, yet he has escaped and knows himself to be safe. He is still immersed in something, though, a certain and specific sort of sadness, like backache but in the brain.

But Caleb? No idea. I watch him. I guess what he is thinking or about to do from his actions but with no more insight than an ordinary mortal. There is something about him that defeats my powers of insight.