‘I know, but… sorry if this sounds petty, but why are you apologising to me instead of to your neighbour, or the parent of this other child?’

‘I thought you’d take it better than either of the other mums. You’re more approachable.’

Great, I thought: punished for good behaviour. ‘Would it make any difference if I said I’d pay double? If I paid whatever the twins’ mum was going to pay you, just to look after Zoe? I will, if that’ll make a difference.’ I shouldn’t bloody well have to, this is outrageous, a voice in my head was shouting. I smiled my most encouraging smile. ‘Pam, I’m desperate. I need someone to look after Zoe that week, and she knows you and really likes you. I don’t think she’d be happy going to someone she doesn’t know so well…’

All the warmth was draining from Pam’s face as I spoke. Watching her eyes, I felt as if I was transforming into something disgusting in front of her, as if my skin was turning to green slime. ‘I’m not trying to rip you off,’ she said. ‘I don’t want more money out of you. What do you think this is, some kind of scam?’

‘No, of course not. I just… look, I’m sorry, Pam, I don’t want to whinge, but I’m a bit upset about this. I can’t believe you can’t see it from my point of view. I’ve got a really important conference that I have to go to. I’ve spent months setting it up. I can’t not go, and Nick needs to work too-he’s used up all his holiday this year. And you’re letting me down for the sake of some woman who wants bigger boobs? Can’t she get her silicon implants another time?’ At no point did I raise my voice.

‘She doesn’t want bigger boobs! She’s having a breast reduction, actually, not that you’d care! Because she’s got chronic backache and it’s ruining her life and her children’s lives, because she can’t get out of her bed some days, she’s in that much agony!’

I started to backtrack and make apologetic noises-of course, if I’d misunderstood, if it was a genuine medical problem-but Pam wasn’t listening. She called me a snobby bitch and said she’d always known I was trouble. And then she started screaming at me to get the fuck out of her face, to leave her alone, that she had never liked me, that she wanted nothing to do with me, never wanted to see me again as long as she lived. Or my family.

I cannot imagine ever yelling at anyone the way Pam yelled at me, not unless they’d harmed my children or set fire to my house. I say this to Esther and she says, ‘Or pushed you under a bus.’ She giggles.

‘She didn’t push me.’ I sigh, pulling my hair away from my neck so that my skin is touching the cool rim of the bath. The water isn’t as warm as I normally have it because it’s so humid tonight and even the idea of hot water on my wounds is painful. ‘If she’d pushed me, she wouldn’t have come over and tried to help, would she?’

‘Why not?’ says Esther. ‘People often do things like that.’

‘Like what? Which people?’ I stir the cloudy water with my toes, annoyed that there isn’t more foam; I should have emptied the bottle. The bathroom is another thing that irritates me about our flat. It’s too narrow. If you sit on the loo and lean forward, you can touch the cupboard door with the tip of your nose.

‘I don’t know which people,’ Esther says impatiently. ‘I just know I’ve heard of that kind of thing before: the guilty party helps his victim in order to look innocent.’ In the background, I hear her microwave beeping. I wonder what she’s heating up tonight-a ready meal or leftover takeaway. A fleeting pang of envy for Esther’s single, hassle-free life makes me close my eyes. She lives alone in a spacious purpose-built flat at the top of a curvaceous, design-award-winning tower block in Rawndesley, with a large balcony that overlooks both the river and the city. Two whole walls of her lounge are made of glass, and-the thing I find hardest to bear-she has no stairs.

‘Anyway, I doubt she was trying to kill you. She probably saw you walking ahead of her, saw a bus coming along, and was so angry that she couldn’t resist. That’d explain why she was all smiles once you’d been hurt-she realised she’d turned her revenge fantasy into reality and regretted it.’

Esther is an enthusiastic imaginer of scenarios. She is wasted at Rawndesley University; she ought to be a film director. Over the years she has been certain that her boss the Imbecile is: gay, a Jehovah’s Witness, in love with her, a Scientologist, a Freemason, bulimic and a member of the BNP. Usually I find her flights of fancy entertaining, but tonight I want seriousness and sense. I’m exhausted. I’m worried about summoning the energy to climb out of this bath.

‘Rawndesley was heaving today,’ I say. ‘Someone could easily have knocked into me by mistake.’

‘I suppose so,’ Esther grudgingly admits.

‘Oh, God. I can’t believe I called Pam an ugly gremlin. I might even have called her evil. I think I did. I’ll have to ring her and apologise.’

‘Don’t bother. She’ll never forgive you, not in a million years.’ Esther chuckles. ‘Did you really call her that? I’m having trouble imagining it. You’re so prim and proper.’

‘Am I?’ I say wearily. There are things about me that Esther doesn’t know. Well, one thing. She once warned me not to tell her anything that really needs to stay secret: ‘If it’s a good story, I won’t be able to resist telling everyone.’ I had the impression she was using the word ‘everyone’ in its fullest sense.

‘So you don’t think I need to… tell the police or anything?’

Esther squawks with laughter. ‘Yeah, right. What are they going to do, appeal for witnesses? I can see the headline now: “The Notorious Bus-pushing Incident of 2007”.’

‘I haven’t even told Nick.’

‘God, don’t tell him!’ Esther snorts, as if I’ve suggested telling my window cleaner: someone entirely irrelevant. ‘By the way, that story about the neighbour and the agonizing back-ache? Complete crap. The woman’s got six-month-old twins, right?’

‘Yeah.’

‘So, she’s been breast-feeding like the clappers and her tits have gone all droopy. She wants to swap them for new, perky ones. The medical gubbins is strictly for emotional blackmail purposes, a way of forcing her husband to part with the cash.’

I hear Nick yelling my name. I ignore him, but he keeps calling me. Normally he gives up almost immediately. ‘I’d better go,’ I tell Esther. ‘Nick wants me. It sounds urgent.’

‘Nick? Urgent?’

‘Unlikely but true. Look, I’ll ring you back.’

‘No, take me with you,’ Esther orders. ‘You know how nosey I am. I want to hear what’s going on in real time.’

I make a rude face at the phone, then balance it on the side of the bath as I wrap a towel round myself. Too late, I realise it’s white and might end up with smears of red on it. I know we’re out of Vanish, so that’s two new items for my list: buy more stain-remover, wash blood out of towel.

I take the phone up to the lounge. Nick is still sitting beside the mounds of shepherd’s pie on the carpet, still watching BBC News 24. ‘Have you seen this?’ he says, pointing at a photograph of a woman and a young girl on the screen. A mother and daughter. Across the bottom of the picture there’s a caption that tells me their names. They are dead; the caption says that too. I try to take it in: the words and the photograph together. The meaning. ‘It’s been all over the news for days,’ said Nick. ‘I keep forgetting to tell you. Not often Spilling makes the national headlines.’

Through a fuzzy layer of shock, I become aware of several things. The woman looks like me. It’s frightening how similar we look. She has the same thick, long, wavy dark brown hair, so brown it’s almost black. Mine feels like wire-wool when it gets too dry, and I bet hers does too. Did. Her face is long and oval-shaped like mine, her eyes big and brown with dark lashes. Her nose is smaller than mine and her mouth slightly wider, and she’s prettier than I am, but still, the overall effect…