I’m about to begin my evening monitoring duties at my bedroom window when my phone buzzes.

I set aside the tray of food I’ve just carried upstairs and stare at the screen. It’s a text, from Holly.

Can you come over asap? Need some advice. H

A warm swell fills my chest. Holly needs some advice and I’m the person she has chosen to ask to provide it.

All I’ve ever wanted, really, is to help.

That was the sole reason I followed Della on the final morning she visited Mr Brown. I tracked her to a coffee shop on the high street. When I walked in a few minutes later, she was crying, mopping at her face with a tissue.

I sat down opposite her, expecting her to tell me to get lost, but when I explained I was Nick Brown’s neighbour and had seen what he’d been up to, stuff just came tumbling out of her pretty rosebud mouth.

She told me everything. How they’d met, how she loved him… which had stung. Imagine loving a buffoon like that!

We met up several times a week after that. There was nothing in it romantically – for her, anyway. But I loved her with all my heart.

I used to sit staring out of my bedroom window, imagining what life might be like, married to Della. Making her happy enough that she might start love me back.

But Nicholas Brown put paid to it all. He had her like a puppet on a string.

One minute it was over between them, the next he’d charmed her back again.

It was very hard to see him giving Della the runaround like that, promising her that he’d leave his wife but clearly having not the slightest intention of doing so.

It all seemed so hopeless. Her emotions were up and down; she didn’t know which way to turn.

So I asked her if she’d like me to try and help her, and she said in what way, and I said I’d have a think about it and let her know.

In the summer, I’d see him fetching and carrying for Mrs Brown, who’d sit morosely in the garden for hours on end. He was so good at assuming the role of the perfect husband.

My rage blossomed like a cherry tree, and over the weeks, it eventually bore fruit.

Mrs Brown was astonished when I turned up at the dental surgery. She stood behind reception, mouth open and eyes wide as I told her everything.

‘They’re at it right now in your bedroom,’ I told her. ‘While you’re here, working your socks off.’

In my fervour to get the facts over to her, I’d quite forgotten about the people in reception and the other staff behind the desk.

Mrs Brown burst into tears, grabbed her coat and bag and ran out there and then.

I sat around for a bit in the reception area like a patient, everyone staring. I didn’t really know what else to do. I felt quite dazed.

Then the practice manager came over and said, ‘I think you’d better leave, sir.’

By the time I caught up with Mrs Brown, she’d already got to Della and they were out on the street with Mr Brown trying to get in between them.

Della was screaming loudly as Mrs Brown attacked her; she was a mere wisp of a thing compared to the older woman. And then Della slapped Mr Brown across the face, calling him a liar and a love rat and he thumped her back. Right in her beautiful face.

And that’s when I couldn’t stop myself… I waded in amongst them, I couldn’t stop punching and kicking, and even when my knuckles were skinned and he collapsed on the floor, I still couldn’t stop hitting him.

The police were called and I ran and it was just a big fat mess.

A couple of days later, Della jumped from the seventh-floor balcony of her new apartment block by the canal. They found a letter to Nick Brown on the kitchen table telling him she couldn’t live without him.

I didn’t go to the funeral. Mother said it would be too unsettling.

I lean forward now in my chair and peer down into Mrs Barrett’s yard, but no one is out there.

People are starting to arrive home from work, using the back door like we do. This is usually my busiest time, recording and monitoring that nothing is amiss, that nobody is acting strangely or out of the ordinary.

But Holly needs me and I decide that this must take priority.

I go back downstairs, plucking my jacket from the hook in the hallway on the way out.

‘David?’ Mother looks up, startled, from stirring a pan as I walk through the kitchen. ‘What’s wrong? Where are you going?’

‘I’m just popping out for a bit,’ I say calmly. ‘I won’t be long.’

‘But…’ She puts down her wooden spoon and turns, her eyes wide. ‘Is everything all right? I mean, you’re not in any trouble, are you?’

‘No. I’m not in any trouble.’ My stomach contracts. ‘Why do you always assume the worst, Mother?’

‘Because you’ve been acting very oddly recently. You keep going out and… Are you going to see that girl next door?’ She spits out the words as if they’re responsible for a nasty taste in her mouth.

If I am, it’s nothing to do with her. I’ve let her control my life for far too long.

‘Your mother asked you where you’re going.’ Brian swaggers towards me as if he’s still a fit thirty-year-old builder instead of a fat mess. ‘You live off your mother like you’re still a ten-year-old, so you’ll be treated like one.’

As I turn to him, the air around me explodes into colours of the rainbow.

I register that Mother is wailing, but that’s fine. I am focused.

I grab Brian by the shoulders and push him as hard as I can. He slips on the kitchen tiles in his sock feet and keels over like a great hog. His head smashes into the wall and I watch, fascinated, as his cracked skull leaves a trail of red down the paintwork.

He doesn’t move. His coarse dirty mouth stays closed and silent. But Mother is screeching in the background like Maria Callas.

I don’t look at her. I just say, ‘I’ll be back soon.’

I step outside into the cool, cleansing air and close the door behind me.

I might be acting fairly calm but my heart is racing and I feel a bit nauseous. But Holly needs my help.

I walk up the side path between the two houses and look directly up at her room. She has the wrong idea about me, thinking I can help her.

I feel disingenuous. Pretending to be something I’m not.

I knock, and Holly comes to the door.

‘Thanks for popping over, David,’ she says, her face pale.

‘Who is it, dear?’ I hear Mrs Barrett call.

Holly rolls her eyes and speaks in a low voice. ‘She’s been a bit confused today. I need to talk to you, in private. Shall we go for a walk or something?’

My chest suddenly feels tight. Perhaps the incident with Brian has unnerved me more than I thought.

‘It’s quite cool out here, and there are a lot of people out and about, so…’

She nods slowly. ‘OK, well you’d better come upstairs then.’

‘Upstairs?’

‘We can’t talk down here. Cora will be interrupting us every few seconds.’ She hesitates and her eyes glisten. ‘And I really need to speak to you, David.’

‘Fine.’ I step inside. ‘Lead the way.’

En route, I pop my head round the living room door.

‘Hello, Mrs Barrett.’

‘David! Come in, sit down, dear. I wanted to ask you if—’

‘David is just going up to measure my room for some shelves, Cora,’ Holly says kindly. ‘We’ll be down soon and then you two can chat.’

Mrs Barrett begins to object, but Holly pulls my arm and guides me towards the stairs.