We were both trembling and I wanted to scream but I knew I had to be strong for Lesley’s sake. I was trying not to think about it, but the red ruin of Brandon Coopertown’s face kept sneaking up on me.

‘Hey,’ said Lesley. ‘Keep it together.’

She was looking concerned, and she looked even more concerned when I started to giggle – I couldn’t help myself.

‘Peter?’

‘Sorry,’ I said. ‘But you’re being strong for me and I’m being strong for you and— Don’t you get it? This is how you get through the job.’ I got my giggles under control and Lesley half-smiled.

‘All right,’ said Lesley, ‘I won’t freak out if you don’t.’ She took my hand, squeezed it and let go.

‘Do you think our back-up is walking from Hampstead nick?’ I asked.

The ambulance arrived first, the paramedics rushing into the garden and spending twenty minutes trying futilely to resuscitate the child. Paramedics always do this with children, regardless of how much it damages the crime scene. You can’t stop them, so you might as well let them get on with it.

The paramedics had just got started when a transit van’s worth of uniforms arrived and started milling around in confusion. The sergeant approached us cautiously – mistaking us for civilians covered in blood and therefore potential suspects.

‘Are you all right?’ he asked.

I couldn’t speak – it seemed like such a stupid question.

The sergeant looked over at the paramedics, who were still working on the baby. ‘Can you tell me what happened?’ he asked.

‘There’s been a serious incident,’ said Nightingale as he emerged from the house. ‘You,’ he said, pointing at a luckless constable, ‘get another body, go round the back and make sure nobody gets in or out that way.’

The constable grabbed a mate and legged it. The sergeant looked like he wanted to ask for a warrant card but Nightingale didn’t give him a chance.

‘I want the street closed and tapped off ten yards in both directions,’ he said. ‘The press are going to be all over this any minute, so make sure you’ve got enough bodies to keep them back.’

The sergeant didn’t salute because we’re the Met and we don’t salute, but there was a touch of the parade ground in the way he swivelled round and marched off. Nightingale looked over to where Lesley and I stood shivering. He gave us a reassuring nod, turned on one of the remaining constables and started barking orders.

Soon after that, blankets appeared, a place was found in the transit van and cups of hot tea with three sugars thrust into our hands. We drank the tea and waited in silence for the other shoe to drop.