The route from house to garage involves a double door, with a slim one-step porch in between. It’s instinct, perhaps self-preservation, but I lunge for the garage light switch and plunge the room into darkness. At the same moment, Dan’s silhouette appears in the doorway. He’s haloed by the light behind; his slim waist and wide, muscled shoulders striking in their athleticism. I’m not used to his new physique.

‘Rose?’ he says, unsure of himself.

I step towards him, stopping him coming down the stairs into the garage. He takes the hint, shifting back into the light of the porch. He’s wearing lounge pants and a loose shirt but they’re uncrumpled and it doesn’t look like he’s been in bed anytime recently.

‘Are you okay?’ he asks.

‘Bit tired, that’s all.’

I can see him clearly but I doubt he can see me, not with the darkness of the garage behind. I’m on the top step, an arm’s length from him, close enough to see his pupils expanding and narrowing as they try to adjust to the light.

‘Why’d you drive home at this time?’ he asks, perfectly reasonably.

‘The hotel bed was too uncomfortable. I was awake anyway, then I saw your text. I figured I could get a few hours’ sleep at home before work later.’

The lie comes so easily that it leaves me a tiny bit wary of myself. Everyone lies: ‘That shirt looks fine,’ ‘Your daughter’s a really good singer,’ ‘No, I don’t mind staying at work for an extra hour.’ They’re white lies to save someone’s feelings, or to maintain a social norm. This feels bigger and yet the words are out of my mouth before I’ve even processed them.

I take another step forward and Dan moves with me, backing through the second door into our kitchen. There’s a dim light glowing through from the living room, not enough for either of us to properly see one another. We’re silhouettes in the murk.

‘Did you check out from the hotel?’ he asks.

‘Yes. Some poor sod was on the night shift. He seemed a bit confused.’

Another effortless lie.

‘How’d the meeting go?’

I’m surprised he remembered why I was away. I was meeting a client, hoping to make a sale – and the offer of a free hotel at the end of it was too much to turn down. I could’ve driven back, of course, but that would have only meant a restless night in bed with Dan, each of us trying not to cross the invisible wall down the centre of our mattress.

‘Fine,’ I reply, even though it definitely wasn’t.

One lie feeds into the next in the same way that one truth would lead into another. It’s not like he really wants to know the answer anyway. It’s been quite a while since we spent the evenings telling each other about our respective days. It’s all small talk now. Good day at work? What did you have for lunch? That sort of thing.

‘Is Liv back?’ I ask.

‘No. I’m sure she’s fine.’

At least we're sticking to that line of answering.

He doesn’t sound as reassuring as I’d want him to be. The safety of a child should be definitive. She’s definitely safe.

‘I’m sure she is, too,’ I reply.

He nods shortly and there’s a moment in which I wonder if we’re thinking the same thing. On the same wavelength, for once. Whatever’s happened between us, she’s still our daughter.

‘I suppose she is eighteen,’ he adds.

‘Did you try calling her?’

‘No answer.’

This is the first time in two years that Olivia has failed to let us know she’s staying out. Sometimes the text comes late – and oftentimes it’s short and to the point – but it’s always there. She was sixteen and I was the typical panicked parent back then. Dan was the cool head. ‘She’ll be fine,’ he cooed – and she was. To a point. She was drunk on cider, probably high on something too, though she always denied it. One of her friends called Dan in the end, asking if he could pick Olivia up because she wasn’t feeling well. It was five in the morning and I’d barely slept. We grounded her, because that’s something you can do – just – when your child is sixteen and underage. At eighteen, you can only ask for a bit of courtesy.

Dan yawns but there’s something odd about it, as if he’s pretending. His hand covers his mouth before he starts and there’s no squinting tiredness to him afterwards.

‘I’m going to go back to bed,’ he says, ‘get another hour before I have to be up for school. Can’t have the kids looking more awake than me.’

He chuckles at his own joke and heads for the stairs, not waiting for a reply. He’s a deputy headteacher, so he has a point – although he’s never been one of those parents whose heads can’t hit the pillow until our child is home.

It’s only when he gets to the bottom of the stairs, directly underneath the light, when I notice the smudge of dirt on his wrist. Dan’s not quite a neat freak and certainly not a germaphobe – but he likes things to be in their place and is the sort to religiously wash hands before meals.

‘What’s on your wrist?’ I ask.

He spins, looking at me and then down to himself. He rubs the mark, only succeeding in spreading whatever it is.

‘I was unblocking the kitchen sink earlier, probably that.’

He shrugs and then he’s gone, not bothering to ask if I’m going to follow.

I call after him to say that I’ll be up in a bit but it’s meaningless. Our bed sharing is more to do with habit than anything else.

The kitchen counter is a good place to lean as I listen to him padding around upstairs. He heads to the bathroom first and the water runs, then he’s off to the bedroom. There are a couple of dull thumps and then quiet. I think about calling Olivia myself, perhaps firing off a text to check she’s all right, but she won’t appreciate it if she is asleep on someone’s sofa. She probably won’t hear or see it anyway, then she’ll get annoyed I was harassing her. I figure I’ll give it an hour.

Back in the garage and I try to work as quickly as I can. There’s a tap that Dan installed, along with a plug in the centre of the garage floor. His thinking was that it would be easier to wash our cars in the winter if we didn’t have to stand out in the cold. His BMW is spotless next to mine, as ever. His car is an extension of him.

I fill a bucket with water and washing-up liquid, but there’s even more blood than I thought. It’s not just on the bonnet, lower windscreen and grill, it’s drizzled down towards the front wheels. There’s mud, too. Lots of it, dried and caked. It clings to the underside of the wheel arches like a leech latched onto flesh. I hate cleaning cars at the best of times. For Dan, it’s therapeutic. He’ll spend a few hours in here clearing his thoughts – or so he says – while shining his car. I don’t think that’s a euphemism. Either way, I prefer to pay a few quid to stick mine through the car wash next to the local Tesco. Can’t really show up with a tenner and a blood-covered car, though.

The first two soapy buckets of water quickly turn a reddish sort of black and disappear down the drain, but I am beginning to get somewhere. The crusts of mud and filth recede, along with any trace of what I’ve done. Or might have done.

When my back starts to ache and my fingers are wrinkled and white, I realise an hour has passed. It’s almost six in the morning and the world will be waking again soon. Dan will be back downstairs.

Now the fog has started to clear, I feel surprisingly awake. It’ll be adrenaline, something like that, but it’s like I’ve had a full and comfortable night of sleep. Those nights where the head hits the pillow and the next thing anyone knows, the sun is up. I’m sure it shouldn’t be like this.

The final bucket of water disappears into the drain; the soapy, filthy suds spinning until there are only a few dregs clinging to the concrete. If I didn’t know better, I could have imagined it all. My car is about as clean as it gets. It’s nowhere near as shiny as Dan’s, but the traces of last night have gone.

It’s only when I step away to examine my handiwork that the phrase slips into my mind. ‘Tampering with evidence’ – that’s what it’s called. It’s what they write in the news reports, what the presenters say on Crimewatch. ‘Police have charged Mr So-and-so for tampering with evidence’.

Is that what I’ve done?

I tell myself that it’s not. That’s not the sort of person I am, and yet, here it is. I’ve acted clinically, barely thinking at all. Act first, think later.

But there wasn’t a crime scene. Was there? If I hit something, then where’s the damage to the car? Where’s the animal – or person – from which the blood came? I looked, I really did. A person can only tamper with evidence if there’s been a crime – and there hasn’t.

I have to tell myself that.

There’s little point in going to bed now and I don’t feel tired anyway.

I head through the house into the kitchen. Olivia’s energy drinks are in the fridge. The ones that are ninety per cent sugar and called things like ‘Carnage’ and ‘Assault’. She knows I don’t approve – what reasonable parent would? – but it is what it is. She could be using worse things to get that buzz.

I think about having one, but my own addiction is a little more acceptable. I fill the coffee machine with granules and water, setting it to fizz and pop as I curl up on the sofa in the living room.

Unsurprisingly, my phone is on its last legs battery-wise. The modern ones are more addicted to power sockets than Olivia is to her energy drinks. I plug it in and then text her, keeping it straightforward and without accusation.

There’s only one thing more valuable to teenagers than money – and that’s free lifts. Olivia failed her driving test a month ago and hasn’t rebooked it. Part of that is for financial reasons, but it’s mainly because she hasn’t handled the rejection well. The reason she failed was, of course, because of the examiner. He gave her confusing instructions, he wanted her to fail, he’d hit his quota for the day. Those sorts of things. There was little point in asking for specifics of what happened because it would be taken as implicit criticism that the reason she failed was something she did, as opposed to a crooked tester.

I scroll through our recent texts, hoping a new one will appear. A minute or so passes and there’s no reply, so I switch to the web browser instead and get back to my own predicament. I search for terms like ‘hit-and-run’, checking the Twitter feeds of the local police forces. No matter how many times I tell myself I couldn’t have hit something, someone, there’s that niggling voice at the back of my mind.

There’s nothing of any particular interest to find. A lorry driver was stopped on the motorway for his vehicle being too heavy; someone else arrested for drink-driving. That’s it. An uneventful night in the real world – certainly no reports of anyone found in a ditch. I want reassurance, but it’s early yet.

The problem is that, as I press back onto the sofa, those three words keep spinning around my mind.

Tampering with evidence.