Even from the doorway, I can see the foreign object inside her mouth. Just like with Rachel, there is a red-and-white friendship bracelet tied around the victim’s tongue. Her head has fallen to one side, her black Cleopatra-style bob revealing grey hinges. Her hair hides half her face, but I still know who she is. I expect everyone here does. The head of the girls’ grammar school is both well-respected and a little feared in the local community.

Helen Wang used to attend St Hilary’s herself as a pupil, and was in the same year as Zoe, Anna, and Rachel. She went from being head girl as a teenager to being headmistress before she was thirty. A high-flying academic with an oversized IQ, and very little patience for people who didn’t share her view of the world. I know that she and Rachel were still friends, and it’s possible that Helen might have known about our affair. If she did, at least she can’t tell anyone about it now.

I don’t need a pathologist to tell me that a knife was used to slit her throat, that much is obvious, but those aren’t the only visible injuries on the body. The victim’s blouse has been undone all the way down to her waist, and the word LIAR has been written across her chest, just above her bra. The letters appear to have been made using a staple gun. There must be over a hundred tiny slivers of silver stuck in her white flesh, spelling the word like metal stitches.

I already feel out of my depth, but nobody else on this team can swim any better. One murder in Blackdown would have been unusual, but two is unprecedented. Even in London, I only worked on an active serial killer case once before. I look around the room, and get the impression that we’re all just trying to tread water, waiting for someone to rescue us. But they won’t. This is it.

I take a step closer and see the white powder on the tip of the victim’s nose.

‘Are we really supposed to believe that the headmistress was a coke head?’ I say.

‘The substance is being tested,’ Priya replies.

When my initial examination of the scene is complete, I step outside, walk back along the corridor, and find the exit that leads to the school playing fields. My hands shake a little as I search inside my coat pocket to find my final cigarette. I think I deserve it now.

I was here when it happened.

I must have been.

I feel almost drunk with tiredness, and everything about the last couple of days seems unreal to me, as though it might be nothing more than a bad dream I can’t wake up from. When I’m done smoking, I head back inside, and walk straight into Priya. It’s as though she must have been standing there, behind the glass door, watching me. I want to know why, but the sound of a school bell drowns out my question before I can ask it.

‘What is that noise?’ I say when it stops.

‘It’s a bell, sir.’

‘Yes, I’m aware of that. Why is it ringing?’ She stares at me as though I might be dangerously stupid, and I feel a shot of bile climb up my throat. ‘The school is closed, isn’t it?’

‘I think so, sir. I expect people will know by now not to come in, having seen it on the news.’

‘You think so? Are you telling me parents haven’t been told not to bring their children here today? What did I tell you, only yesterday, about securing crime scenes?’

She looks down at the floor. I know how badly she wants to impress me, and how upset she feels whenever she gets something wrong, but I can’t always let things go.

‘It’s OK. Just go to the school secretary’s office now, and make sure they tell parents and all staff to stay away until further notice – not everybody watches the news – and put a couple of uniforms on the front gates, just in case. Also, if you see that BBC team, ask them to leave the car park. They shouldn’t be on school property without our say so. I don’t know how they got here so fast, but they can bloody well report from the street like everyone else.’

‘Sir, I should probably—’

‘Can you please just do as I’ve asked?’

She nods and retreats down the corridor. I step back outside for a moment, I need some more air before I can face going back into that room. Everyone expects me to know what to do, but this is new even for me. Things can get a little dark when the blind lead the blind.

I stare at the school playing fields, which slope down to the woods below. As the crow flies, we are probably less than a mile from the spot where Rachel was killed. When I hear footsteps approaching on the path behind me, I presume it is Priya again.

‘Did you get it done?’ I ask.

‘What do you mean?’

I turn and see Anna. ‘What are you doing here?’

‘Your sidekick sent me around this way to find you.’

‘Priya? Why would she do that? And how did you get here so fast? There have been no statements to the press as far as I know, and I would know because it would be me making them.’

Anna doesn’t answer. I glance over my shoulder to check that we are alone and can’t be overheard.

‘Why were you wearing that cotton bracelet yesterday?’ I whisper.

She looks as though she might laugh.

‘Why do you keep asking me about that?’

‘Where did it come from?’

‘It’s none of your—’

‘I’m telling you this because I still…’ love you. That’s what I was about to say. While I know it’s true, I also know I can’t tell her that. Sometimes love is keeping your feelings to yourself. ‘I still worry about you,’ is what I settle on. She smiles, but my irritation levels have already exceeded the recommended daily limit. ‘I’m serious, Anna.’

‘You’re always serious. It’s one of your many flaws.’

‘I mean it. If you repeat what I’m about to tell you to anyone else, or dare to report it—’

‘OK, calm down, I’m listening.’

‘Good, I hope you are. Both dead women were found with friendship bracelets, just like the one you were wearing, but inside their mouths. Tied around their tongues.’

She turns visibly pale, and I’m glad the information has caused some kind of emotional response. I would have been deeply troubled if it hadn’t. I don’t like feeling as though I didn’t really know the woman I was married to for all those years.

‘So why do you have one?’ I ask, hoping to get an answer this time.

‘I don’t, I’ve lost it.’ It sounds like a lie, but she looks like she is telling the truth. ‘You sent me a text in the middle of the night saying you wanted to talk, was that why—’

I’d forgotten I had drunk texted her.

‘It was early this morning – hardly the middle of the night – and this really doesn’t seem like the time or place. You haven’t answered my questions. Any of them—’

‘Why did you text me, Jack?’

She looks towards the doors leading inside the school – still thinking about the story first, I see – and I steer her away.

‘I really don’t have time for this right now, in case you can’t tell. I just wanted to say that I wouldn’t get too close to your colleague if I were you.’

She stares at me, her mouth forming a perfect little O.

‘Just so I understand this, you’re dealing with a double murder, but what you’re really worried about is me sleeping with my cameraman?’