The conversation was somewhat stilted because I was tired and Aidan was understandably nervous and uncomfortable. The strain was getting to us both and it was impossible to relax.

I couldn’t stop thinking about Dave Prentiss and Marion Nash. And those vile text messages.

‘Do you think there will be another murder tonight?’ Aidan asked me.

It was the same question every copper in London would be asking themselves. There had been two killings over two days. Did that mean the perp was planning to carry on at that rate?

‘I just don’t know,’ I said truthfully. ‘But it must be less likely now that there’s some form of protection for all those who’ve been threatened.’

But no amount of protection could stop anyone from falling victim to a determined hitman. I knew that and I was sure that Aidan did as well. But I chose not to say it out loud.

Instead I told him about our conversation with Eddie Fowler and what he’d revealed to us about Roy Slack.

But I was sorry I did because it provoked an angry reaction.

‘I can’t believe you haven’t locked the bastard up,’ he seethed. ‘If you think he’s the one behind this then you should have arrested him.’

‘It’s not as straightforward as that,’ I said. ‘We need proof and we don’t have it.’

‘You lock up suspected terrorists without proof,’ he said. ‘So what’s the difference?’

‘The difference is we know that Slack is not committing these murders. He’s under continued surveillance. And placing him in custody probably wouldn’t stop the killings or the threats anyway.’

‘Then how are you going to bring all this to an end, Laura? How high does the body count have to go before the police take some serious fucking action?’

I didn’t want to get into an argument so I stood up and started clearing the dishes. Aidan went to the fridge, took out a bottle of wine and poured some into a glass, which he carried into the living room. He was fuming and I didn’t blame him.

I decided to give him time to calm down before joining him. I filled the bowl with warm water and began washing up by hand since we’d only used a couple of plates.

And that was when I thought I heard something outside. It sounded like an object had been knocked over in the garden. My first thought was that next door’s cat had come through the fence and was skulking around again.

But then I suddenly experienced a twist of alarm. Supposing it wasn’t the cat? Supposing there was someone out there?

I felt every muscle in my body go stiff as I stepped quickly across the room to switch off the light, plunging the kitchen into darkness.