My throat is dry and my feet are starting to ache. I decide it can’t hurt to go back to the car, where I’m sure there’s an old bottle of water lying around in one of the footwells or wedged under a seat. At least three people have assured me that Jenny Naismith won’t leave until at least four o’clock, so I can afford to have a break.

Outside, I switch on my phone and listen to four messages, two from Esther and two from Natasha Prentice-Nash. I delete them all, then key in the number Sian gave me. A chirpy female voice with a Birmingham accent says, ‘Hi, I can’t take your call at the moment, but leave a message and I’ll get back to you.’ I swear under my breath and toss the phone back in my bag. I can’t bear to wait and do nothing. I need everything to happen now.

Sian ’s words buzz around my worn-out brain. I try and fail to make sense of everything I now know: bossy, literal-minded Lucy Bretherick with her perfect family, her adoring parents who wanted nothing but her happiness, who held hands all the way through parents’ evenings; and Lucy’s two friends, both from families that sound not quite so perfect… Yet Lucy is the one who ends up dead. Murdered by her mother. I think about envy, how it is fed by inequality.

Amy’s old nanny runs our after-school club. That was what Sian said. Old as in she’s no longer Amy’s nanny? Why not? If the Olivers moved away, why didn’t they take her with them? I’ve got friends and colleagues who would cut their own limbs off sooner than lose a trusted nanny.

I wish I’d thought to ask Amy’s mother’s name and the name of the bank she works for. Amy’s mum, Oonagh’s mum-did Sian mention any of them by name? It drove me mad after Zoe was born, the way I quickly became ‘Zoe’s mummy’, as if I had no identity of my own. To annoy the midwife and the health visitor I used to make a point of calling Zoe ‘Sally’s daughter’. They had no idea why I was doing it and looked at me as if I was insane.

Sian said ‘worked’, not ‘works’-Amy Oliver’s mother worked for a bank in London. That’s what you say when you haven’t seen someone for a while, when you’re describing what they did or how they were when you were last in touch with them. There’s nothing unusual about it. So why do I fear that the Oliver family has vanished off the face of the earth?

I’m halfway across the car park when I catch sight of my Ford Galaxy. There’s a jagged silver line across the paintwork, stretching the length of the car. The two tyres I can see are flat, and there’s something orange lying behind one of the wheels. I swing around, breathing hard, expecting to see a red Alfa Romeo, but the only other cars in the visitors’ car park are three BMWs, two Land Rovers, a green VW Golf and a silver Audi.

I move closer. The orange lump is a ginger cat. Dead. Its eyes are open, in a head that’s no longer attached to its body. There’s a red mess where its neck should be. A rectangle of brown parcel tape has been stuck over its mouth. I bend double, retching, but nothing comes up; there’s nothing in my body apart from sharp fear. Dark spots form on the insides of my eyes.

This is when it hits me: someone wants to harm me. Oh, God, oh, God. Boiling-hot panic courses through me. Someone is trying to kill me and they can’t, they absolutely can’t because I’ve got two young children. After a few seconds I come down from the wave of high-pitched terror and feel only numb disbelief.

I need water. I fumble for my car keys, realise I forgot to lock the damn thing and drop them back in my bag. Keeping my head turned so that I don’t have to see the cat, I struggle to open the driver door. My arms and hands have no strength; it takes me three tries. Once I’ve done it, I look under the driver’s seat and the front passenger seat for my bottle of water. It’s not there. I’m about to slam the door when I notice it sitting upright on the passenger seat. I blink, half expecting it to disappear. Thankfully it doesn’t. Standing with my head tilted back, I pour what’s left of the water into my mouth, glugging it down, spilling some on my neck and shirt. Then I lock up the car and, without looking back at the cat, start to run towards the centre of town.

Brown parcel tape over its mouth. A warning to me to say nothing. What else could it mean?

I run until I get to Mario’s, Spilling’s only remaining cheap and cheerful café. Its owner, who has two-tone black and white hair like a skunk, sings opera arias at the top of her voice all day long and thinks she’s being ‘a character’. Usually this makes me want to demand a discount, but today I’m grateful for her tuneless outpourings. I force a smile in her direction as I walk in, order a can of Coke so that she’ll leave me alone, and find a table that’s not visible from the street.

First things first: phone nursery to check Zoe and Jake are all right. I am barely able to sit still as I listen to the ringing. Eventually one of the girls answers and tells me my children are fine-why wouldn’t they be? I almost ask her to check the street outside for dead cats, but I manage to restrain myself.

I’m not scared of you, you bastard.

I open my Coke and take several big gulps that fill my stomach with uncomfortable air. Then I pull two pages out of my notebook and start to write another letter to the police. I write quickly, automatically, without allowing myself to stop and think. I’ve got to get it all down on paper before the dizziness at the edges of my mind gets any worse. I grip the edge of the table, a pins and needles sensation prickling the skin all over my body. I really ought to eat something. Instead, I write and write, everything I think the police need to know, until I can no longer ignore the twitching in my throat. I’m going to be sick. I grab my letter and my bag and run to the ladies’ toilet, where all the Coke I’ve drunk comes back up. Once my stomach is empty, I close the toilet lid, sit down and lean my head against the partition wall. It occurs to me that I could collect Zoe and Jake early today. I’m not working; I could go and collect them now.

My letter isn’t finished. I wanted to write more, but I can’t remember what. Strange, dark shapes move in front of my eyes, blurring my vision. I open my bag and pull out a white envelope that has been in there for at least a year. It’s addressed to Crucial Trading, the carpet company. I was supposed to fill in a customer satisfaction questionnaire and return it to them. Nick and I spent seven thousand pounds on new wool carpets and leather and sisal rugs for our lovely old house, before we went mad and decided we needed to move next door to Monk Barn Primary School. This makes me cry. Then I realise I can’t collect Zoe and Jake because my car tyres have been slashed, and cry harder.

I pull the uncompleted questionnaire out of the envelope, put my letter in, cross out Crucial Trading’s name and address, and write ‘POLICE’ in capital letters. I can’t manage any more than that one word. Stumbling back to my table, sweating, I admit to myself that I am seriously unwell. It must be the shock. I should pick up the kids and get home before I start to feel worse. ‘I need a taxi,’ I say to skunk-opera woman.

She eyes me with suspicion. ‘Rank is outside health shop,’ she says. ‘You no eat?’

‘Sally?’ A deep, male voice comes from behind me. I turn and see Fergus Land, my next-door neighbour. He beams at me, jolly as ever, and I feel even weaker. ‘I can give you a lift,’ he says. ‘Are you going home? Not working today?’

‘No. Thanks,’ I force myself to say. ‘Thanks, but… I’d rather get a taxi.’

‘Are you all right? Gosh, you’re a bit off-colour. Been overindulging? Celebration last night, was it?’

He looks so kind, so concerned. If he offered to drive me to nursery and then home in silence, I’d gladly accept, but I can’t face the prospect of making conversation.

‘Did you tell Nick I’ve got his driver’s licence? He hasn’t-’