Outside the night air was thick and humid, great dark clouds clustering overhead, having blown in from the west during the day. There was still a winter edge of cold, but when you walked you were warm and the air felt soft on your face.

‘Leave the car,’ Sally said when they came out of the apartment block. ‘We can walk and then take the Métro. It’s a good night for walking.’

Bannerman allowed her to take his arm and they walked the length of the Rue de Commerce and turned up into the Rue de la Loi.

‘I suppose you must feel pretty bad about the kid,’ she said. He gave no sign that he had heard her. ‘They can be that way sometimes, autistic kids. Some worse than others. A break in the routine, a stranger, or maybe a pet phobia. Any of these can set them off on a screaming fit. Sometimes it can last an hour, or two hours, or even more. But they always come through.’

Bannerman kept an even pace and did not look at her. Ill-pasted posters flapped on the hoardings, behind which workmen sweated under floodlights on excavations for the foundations of yet another office block. ‘What’s she like?’ he asked. ‘The kid.’

Sally swept her hand through a vague gesture. ‘It’s difficult to know. She doesn’t speak, you see. It’s not that she can’t, physically I mean. It’s just that . . . well, she doesn’t. She can write a little when the mood takes her, but she can’t construct sentences. She gets what she needs by gestures. A kind of sign language. But you’ve got to know her pretty well to understand it. The doctors say she comprehends what’s going on around her, but her only positive responses to anything are the fits. She takes it all in, but she can’t seem to communicate what any of it means to her.’

Bannerman tried to imagine what that might be like. To be trapped inside yourself. Your body a cage. The world can come in but you can’t get out. He conjured the child from his memory of her. Straight-cut shoulder-length brown hair. A small, plain, expressionless face dominated by large, dark eyes. A grey jumper and skirt. Heavy black shoes. Clumsy limbs.

‘But she can draw like I’ve never seen a child draw,’ Sally said. ‘Fantastic living drawings that she does with a pencil. Drawings that leap out of the page at you. She has this tremendous sense of depth and perspective. A compensation, maybe, for everything else she lacks. They’re worth seeing.’