Dalgliesh went over and the paper was signed. He and Kate picked up their coats and were ready to go. As if they were parents who had come to discuss the progress of their children, Collinsby said formally, “It was good of you to come to the school. I’ll see you to the door. When you need to speak to me again, no doubt you’ll be in touch.”

He unlocked the front door and went with them to the gate. The last they saw of him was his pale taut face staring at them from behind the bars, like a man incarcerated. Then he closed the gate, turned, walked with firm steps to the school door and entered without looking back.

In the car, Dalgliesh switched on the reading light and took up the map. He said, “The best route seems to be to take the M1 south, then the M5 and the M3. You must be hungry. We both need to eat, and this doesn’t look a particularly promising place.”

Kate found herself desperate to get away from the school, from the town, from the memory of the last hour. She said, “Couldn’t we stop somewhere on the motorway? I don’t mean for a meal, but we could pick up a sandwich.”

The rain had stopped now except for a few heavy drops which fell, viscous as oil, on the bonnet. When they were at last on the motorway, Kate said, “I’m sorry I said what I did to Mr. Collinsby. I know it’s unprofessional to sympathise with a suspect.” She wanted to go on, but her voice was choked and she simply said again, “I’m sorry, sir.”

Dalgliesh didn’t glance at her. He said, “You spoke out of compassion. To feel compassion strongly can be dangerous in a murder investigation, but not as dangerous as losing the capacity to feel it at all. No harm was done.”

But the tears still came and he let her quietly weep, keeping his eyes on the road. The motorway unwound before them in a phantasmagoria of light, the procession of dipped headlights on their right, the moving pattern of the southward traffic, the blotting out of black hedges and trees by the huge shapes of trucks, the roar and grind of a world of unknowable travellers caught up in the same extraordinary compulsion. When he saw a sign saying Services, Dalgliesh moved into the left-hand lane, and then pulled off onto the slip road. He found a space on the edge of the car park and switched off the engine.