I lay there for a long time, trying not to worry, trying to tell myself it didn’t matter, that I was insane to think what I was thinking.

But I couldn’t get it out of my mind.

So I finally got up and sneaked out of the bedroom and, feeling like a thief in my own house, headed for the den.

I closed the door, turned on the desk lamp and took a quick look to see if the dot was still there. It was.

I opened the desk drawer and hunted for a pencil and couldn’t find one, but I finally found one of Bill’s crayons. I got down on my knees and carefully marked the floor around the desk legs, so that, if the desk were moved, I could put it back again.

Then, pretending I had no particular purpose for doing it, I laid the crayon precisely on the dot.

In the morning, I sneaked a look into the den and the crayon was still there. I went to work a little easier in my mind, for by then rd managed to convince myself that it was all imagination.

But that evening, after dinner, I went back into the den and the crayon was gone.

In its place was a triangular contraption with what appeared to be lenses set in each angle, and with a framework of some sort of metal, holding in place what apparently was a suction cup in the centre of the triangle.

While I was looking at it, Helen came to the door. “Marge and I are going to see a movie,” she said. “Why don’t you go over and have a beer with Lewis?”