I wanted to ask more questions, but Drummond said he had more calls coming through and would ring me later.

When I came off the phone it felt as if my heart was flinging itself against the wall of my chest.

‘Sit down and let me get you a cup of coffee,’ Sergeant Wilks said, so I nodded and sat down on the sofa.

The assassination of John Saunders was a staggering development. And totally unexpected. He wasn’t just another detective investigating organised crime. He was – or had been – the highest-ranking police officer in the country. The Commissioner of the Met, no less. The man in charge of a force that consisted of more than 40,000 staff, including 33,000 regular police officers.

The job didn’t just entail leading the fight against crime in the capital. The Commissioner was also responsible for counter-terrorism and the protection of the Royal Family and senior government ministers.

His death at the hands of an assassin would have huge ramifications and be headline news around the world. It was going to spark a major debate about protection for senior officers and politicians. And it would plunge morale within the Met to an all-time low.

Sergeant Wilks handed me a Styrofoam cup filled with steaming black coffee, then told me he was going to resume his position in the corridor.

‘I won’t be leaving here just yet,’ I told him, having changed my mind about going to my mother’s house. ‘I don’t know how long I’ll be staying.’

After he had left the room I was consumed by a strong sense of unease. I remained seated on the sofa, not moving even to drink my coffee. My muscles felt as though they’d been injected with lead, which was probably my body reacting to yet another shocking event.

I was convinced now that this wasn’t just about the organised crime task force. I suspected the killings would continue even if the Met closed it down. This was aimed at every police officer in London, and the death toll was certain to rise.

So who would be next? Another detective? A family member? My mother? Me? Or would it be someone like the Mayor of London, to whom the Commissioner reported on matters relating to crime and policing?

The more I thought about it the harder it was to keep from screaming out loud. It got to the point after about twenty minutes where it seemed like the walls were closing in on me.

I set my untouched coffee on the table and got up to return to Aidan’s room, where I’d now decided to spend another night. I couldn’t bear the thought of leaving him by himself, even though he was on the road to recovery.