It’s Sunday, and Dominic has gone out again, leaving me and Daisy alone. He was back by three thirty yesterday afternoon, so at least we got to spend some of the day together, but the hours in between dragged terribly. I’m in a no-win situation. If I tell him I don’t want him to train, I come across as a nagging, clingy wife; if I give him my blessing, I’m left on my own every day for six weeks. And I’m pretty sure this won’t be the last event he’ll enter. There will be more triathlons, more training. Am I being unreasonable? I honestly don’t know. All I do know is there’s a chasm of emptiness opening up before me, and I’m falling into it, spinning over and over, down and down and down.

Daisy has started making little frustrated noises, she’s hot and bothered, irritable, so I take her out onto the lawn with some of her toys and we sit under the sun umbrella, taking advantage of the half-hearted breeze. I pull her onto my lap so she’s facing me, managing to find a little comfort in her wide-eyed smile. I bounce her up and down but my heart isn’t in it. All I want to do is go back to bed. To sleep away my loneliness. How can I be feeling such despair when on the surface of things I have everything I ever wanted? What has changed?

A Greek philosopher once said that the only thing that is constant is change. Well, I don’t want things to change. I want what Dom and I have to remain the same. Our strong relationship, the safety and comfort of our house. I realise that since I heard those voices in the monitor four days ago, I no longer feel comfortable in my own home. I’m scared to be here alone. Maybe that’s why I’m resentful of Dom’s training. I don’t know. I don’t trust what I’m feeling. I don’t understand it.

It’s as if outside influences have moved in and taken over. Made me uncertain of everything. Made me suspicious, untrusting. I look at the sky, at the distant trees, at the grass, and instead of filling me with calm, they mock me with their other-ness. An imperceptible change that only I can sense. The blue of the sky has turned harder, colder, more remote. The leaves on the trees whisper treachery and wickedness. The green of the grass appears an unnatural hue, as though it isn’t real. I shake my head to dislodge these thoughts. There must be something wrong with me. Maybe I’m ill, or maybe I’m simply suffering with an overactive imagination, the heat of the sun addling my brain.

The doorbell snaps my thoughts back to reality. Whoever it is can go away. I don’t trust myself to have a normal conversation with anyone right now. I bring Daisy close to my chest, inhaling the milky scent of her hair. My whole body tenses as the doorbell chimes once more. I want to scream at it to shut up. To tell whoever it is to leave me alone. But it rings again. They’ll have to give up eventually, surely. I begin counting, silently mouthing the numbers. When I reach sixty and there have been no further doorbell chimes, I exhale in relief. Whoever it is must have gone.

I need to go inside to check the locks. As I rise to my feet a voice makes me jump so violently I almost drop Daisy.

I shriek.

‘Kirstie, I do apologise if I startled you.’

I glance across to the fence, where I see Martin’s bespectacled face peering over at me.

‘Jesus Christ, Martin, you scared the life out of me.’

‘I did try ringing the doorbell, but no one answered. I presumed you must be in the garden, unable to hear it.’

‘What do you want?’ I ask through clenched teeth, letting out a silent scream in my head that echoes through every fibre of my body.

‘Apologies for disturbing you on a Sunday morning. But I wondered if I could call on you to accompany me next door. It won’t take long.’

‘Again?’ I ask. ‘You want me to come over to your house?’

‘Actually, no.’ His face flushes and he lowers his voice. ‘I was hoping we could pop into number six’s garden while the builders are away. I want to check the extension measurements against the plans which I managed to acquire from the council yesterday.’

‘Isn’t that trespassing on private property?’ I say.

‘You’re right, Kirstie,’ Martin replies, the crimson hue in his cheeks deepening even further. ‘But, if what I suspect is correct, then those builders are flouting planning permission by building closer to my boundary wall than has been permitted.’

I don’t reply, frantically trying to think of an excuse. If only I hadn’t come outside, he wouldn’t have had the opportunity to ask me.

‘So you’ll pop round, Kirstie? You and the little one?’

Annoyingly, no excuses are coming to mind.

‘Actually, if you come to mine first we can look at it from my garden. Then we’ll nip to number six to take the measurements.’

‘Okay,’ I say, furious with myself for not saying no.

‘Wonderful. See you in a minute, Kirstie.’

Once his face has disappeared from view, I roll my eyes and haul myself to my feet, silently cursing my neighbour.

On the way over to his place, I remember the fact that Martin has a basement in his house. It’s stupid and paranoid of me to worry about this. Martin has lived there for years and we’ve been his neighbours for as long as we’ve lived here and never had reason to suspect anything untoward. But the fact remains that I never knew about the basement until this week. Was it built at the same time as the house? Or did he have it constructed after he moved in?

The silence out here today is unnerving. Ironically, I wish the builders were back, shouting and hammering and drilling. I can’t even hear any birds singing, just the swish of my dress as I walk and the dull thump of my heartbeats.

I begin to speculate about what is down in that basement. Is it used for storage? Is it an extra living room? I can’t help more sinister thoughts creeping in. Maybe it’s some sort of torture chamber or prison cell? Does he keep girls prisoner like in all those news stories? I shudder and tell myself not to be so silly.

Martin opens his front door as Daisy and I walk up the path. ‘Remember; shoes.’ Martin says.

I want to take them off and lob them at his head, but instead I dutifully remove them before walking into his claustrophobic house, its stink of pine air freshener making me want to gag.

‘It’s a shame about that young couple,’ Martin says, shaking his head. ‘You know, the Cliffords at number two.’

I follow him into the kitchen and through to his back garden, refusing to be drawn into the conversation, but he carries on anyway, even without a prompt from me.

‘Have you noticed, they’re always having people round? And their visitors park extremely inconsiderately up on the kerb or over the neighbours’ driveways. I’ve seen them park over your drive, Kirstie. You should let them know it’s not acceptable.’

‘I’ve never noticed,’ I reply.

‘Well I have,’ he says sagely. ‘I leave notes on their windscreens but they don’t seem to pay any attention.’

I blow air out through my mouth, trying to tune out his moaning. It doesn’t normally bother me, but today it’s winding me up to the point where I want to yell at him to shut up.

‘Also,’ Martin continues, lowering his voice, ‘I don’t want to poke my nose in where it’s not wanted, but I thought you should know your husband is spending a lot of time at the Cliffords’ house.’

‘What are you talking about?’ Dom and I are always friendly towards the young couple who live at number two, but I wouldn’t necessarily say we were actual friends. And Dom’s never mentioned going over there.

‘Well, I don’t like to tell tales out of school,’ Martin says with an apologetic shrug, ‘but I’ve seen young Dominic coming in and out of their house quite a lot.’

‘What do you mean by quite a lot?’ I snap.

‘Maybe four or five times. It’s usually just after he gets home from work. But I’ve seen him there at weekends, too.’

I want to tell Martin to mind his own bloody business, but I also want to find out what he’s talking about. ‘How long does he spend over there?’ I ask, hating myself for digging up gossip about my own husband from Martin, of all people.

‘Hmm, I’m not sure. Not long. It’s not as though I’m timing him or anything.’ He gives a low chortle and I think to myself that, actually, Martin probably is the type of person who would time him. ‘A few minutes or so would be my guess,’ he adds.

‘Well, I’m sure Dom was just being neighbourly,’ I say, wanting to erase the gleam in Martin’s eye. He must be aware that he’s unsettled me with his revelation.

‘Well I don’t trust those two,’ he says. ‘You want to tell young Dominic to watch himself. They’re a noisy, flighty pair and there’s something shifty about them.’

‘They’re just a… carefree, fun-loving couple, like most people in their twenties,’ I say.

‘Hmm.’ Martin crosses his arms over his chest.

‘Anyway,’ I say, keen to get this visit over with, ‘what is it you want me to look at here?’

‘Ah, yes. I have the plans this time, so we can prove my theory is correct.’ He waves a sheet of paper triumphantly in the air. ‘Like I said before, I’m worried that the underpinning for next door’s extension is having an effect on my foundation. I think they’ve built it too close to the boundary line.’ Martin drones on for several more minutes, pointing out heights and elevations and jabbing his finger onto various areas on the plan.

I cut him off. ‘Shall we go next door and measure up?’

‘Good idea, Kirstie. Let’s get hard evidence.’

I shift Daisy to my other hip and follow him back through the house towards the front door. As we pass through the hall, Martin stops to push the open cellar door shut, but not before I catch a glimpse of carrier bags piled up at the top of the basement steps. I recognise the logo – they were Toy Shack carrier bags. Why would Martin have bags from a toy shop?

My heart begins to thump uncomfortably. Martin doesn’t have any children or grandchildren, unless you count that creepy doll that belonged to his late wife. I stop where I am. I have a bad feeling.

‘Come on, Kirstie,’ Martin says, turning back to face me. ‘Why have you stopped there? Something the matter?’ He smiles, showing those yellow teeth, and a sudden wave of nausea sweeps across me. Who is this man, my neighbour? I don’t really know him, yet here I am alone in his house with my baby. No one else even knows I’m here.

With a start, I realise that the Toy Shack also sells baby stuff – formula, nappies.

What if he’s got a real baby down there?

That could have been the crying I heard the other day. Oh my God! Our neighbour could be a psycho. Get out of here, screams a voice in my head. Get Daisy away from him.

‘I’m sorry, Martin,’ I say, my voice strangely calm and steady, ‘I’ve just remembered something really important. I’ve got to go.’

‘What? Now? But we haven’t—’

‘Sorry.’ I cut him off.

‘You can’t go,’ he says. ‘You said you’d help me.’

My gaze is now locked on the front door ahead of us. I should have waited until we were outside to give my excuses. In here, he can bar my exit. I tamp down the terror in my throat and take a step towards him, wondering if he is going to try and physically stop us from leaving his house.

I sidle past him, holding my breath and trying not to cry. Then, I pull open the front door and pray he doesn’t try to grab at us.

‘I need you to come with me, Kirstie,’ he says, his hand coming down to rest on my bare shoulder.

With a squeal, I shrug him off and stumble outside. I begin to run down his driveway without stopping to put my shoes back on, praying he doesn’t follow us but too scared to turn around and check. I must have been mad to go round there on my own. What was I thinking? I need to get home. I need to lock all the doors and windows, to close the curtains so we’re safe from prying eyes. I’ll have to leave everything out in the garden – Daisy’s toys, my mug of half-finished tea. It’s not safe for me to go out there even for a moment. Martin could easily climb the fence. He could take my daughter and put her in his basement. My body is hot and cold, I can barely breathe. Can it be true? Can I be living next door to a psychopath?