Greg and I had argued about stupid things. Whose turn it was to empty the rubbish bin. Why he didn’t rinse the basin after he’d shaved. Why I didn’t know how irritating it was when I cleaned up around him, huffing just loudly enough so that he’d hear me. When he interrupted me in the middle of a sentence. When I’d used up all the hot water. We argued about clothes that shrank in the wash, botched arrangements, overcooked pasta and burnt toast, careless words, trivial matters of mess and mismanagement. We never fell out over the big things, like God or war, deceit or jealousy. We hadn’t had long enough together for that.

‘So you don’t believe me?’

Mary and I were walking on the Heath. It was cool and grey, the wind carrying a hint of rain. Our feet shuffled through drifts of damp leaves. Robin, her one-year-old, was in a carrier on her back; he was asleep and his bald, smooth head bobbed and lolled on her neck as we walked. His pouchy body swung with each step Mary took.

‘I didn’t say that. Not exactly. I said…’

‘You said, “Men are such bastards.”’

‘Yes.’

‘Meaning?’

‘Meaning that men are such bastards. Look, Ellie, Greg was lovely.’

‘But?’

‘But he wasn’t a saint. Most men stray if they get the chance.’

‘Stray?’ I said. I was beginning to feel angry and rattled. ‘Like a sheep that’s got out of its field?’

‘It’s all about opportunity and temptation. This Milena probably made the first move.’

‘This Milena didn’t have anything to do with him. Or him with her.’

Suddenly Mary stopped. Her cheeks were blotchy in the cold. Over her shoulder Robin’s eyes opened blearily, then closed again. A thread of saliva worked its way down his chin.

‘You don’t believe what you’re saying, do you?’ she said. ‘Not really.’

‘Yes, I do. Though you clearly don’t.’

‘Because I don’t agree with you, it doesn’t mean I’m not on your side. Are you trying to push us all away? It’s rotten, what’s happened. Really horrible. I have no idea how I’d be dealing with it in your situation. Listen, though.’ She put a hand on my arm. ‘I do have a bit of an understanding of what you’re going through. You know Eric? Well, obviously you know Eric. You know what happened just after Robin was born – and when I say “just after”, that’s what I mean. Three and a half weeks, to be precise.’

A feeling of dejection settled on me.

‘He slept with this woman at work. I was woozy and weepy and tired, my breasts were sore, I’d only just had my stitches out so I could hardly sit down, sex was out of the question – I was a moony, overweight cow. And yet I was happy. I was so happy I thought I’d melt. And it wasn’t just once, a drunken mistake or something, it went on for weeks. He’d come home late, take lots of showers, be over-attentive, over-irritable. It’s such a bloody cliché, isn’t it? Looking back, I can’t believe I didn’t realize what was going on. It’s not as if the signs weren’t there. But I was blind, in my own little bubble of contentment. I had to practically see them together before I knew.’

‘Why didn’t you tell me before?’ I remembered again the conversation with Greg, in which I had insisted I would have known if Eric had been unfaithful to Mary.

‘Because I felt humiliated. And stupid.’ She glared at me. ‘So fat and ugly and useless and ashamed. You must understand that feeling now, after what’s happened to you. That’s why I’m telling you.’

‘Mary,’ I said, ‘I’m sorry. I wish we’d talked about it before. But it’s not the same.’

‘What makes you and Greg so different?’

‘He wouldn’t have behaved like that.’

‘That’s what I used to say about Eric.’

‘I have an instinct.’

‘You can’t face the truth. I’m your friend. Remember? We can tell the truth to each other, even if it hurts.’

‘It doesn’t hurt because it’s not true.’

‘Has it occurred to you that maybe he was sick of having sex to get pregnant?’

I couldn’t stop myself: I flinched in pain, as if Mary had slapped me across the face.

‘Oh, Ellie.’ Her face softened; I saw there were tears in her eyes, whether from the cold or emotion I couldn’t tell.

WPC Darby showed me into a small room. There were red and pink plastic flowers in a jug on the desk, and more flowers – yellow this time, a copy of Van Gogh’s Sunflowers – in a framed picture on the wall. I sat down and she sat opposite me, folding her hands on the desk. They were broad and strong, with bitten nails. No rings on her fingers. I looked at her face, weathered, shrewd and pleasantly plain under her severely cut hair, and was satisfied that she was the right person to tell. There was some meaningless chat and then I stopped.

‘It’s not the way it seemed,’ I said.

She leaned towards me slightly, her grey eyes on my face.

‘I don’t believe he was having an affair with Milena Livingstone.’

Her expression didn’t waver. She just went on looking at me and waiting for me to speak.

‘Actually I don’t think they even knew each other.’

She gave a nervous smile and when she spoke it was clearly and slowly, as if I was a small child. ‘They were in the same car.’

‘That’s why I’m here,’ I said. ‘It’s a mystery. I think you ought to look at it again.’

In the silence, I could hear the voices in the corridor outside. WPC Darby steepled her fingers and took a deep breath. I knew what she was going to say before she said it.

‘Ms Falkner, your husband died in a car crash.’

‘He wasn’t wearing his seatbelt – but Greg always wore it. You have to investigate further.’

‘The coroner was perfectly satisfied that it was a tragic accident and that no other vehicle was involved. I understand that the fact he was with another woman is unsettling and upsetting for you. As a matter of evidence, how they knew each other doesn’t matter.’

‘There’s no evidence at all, of any kind,’ I said. ‘Nothing to show that he knew her.’

Again, I anticipated what she was going to say. ‘If he was having an affair and keeping it secret, then perhaps that’s not surprising.’

‘I’m telling you, he didn’t know her.’

‘No. You’re telling me you don’t believe he knew her.’

‘It amounts to the same thing.’

‘With all due respect, it does not. What you believe and what is true are not necessarily the same thing.’

‘So you’re just going to let things lie?’

‘Yes. And I would advise you to do the same. You might consider seeing someone about -’

‘You think I need bereavement counselling? Professional help?’

‘I think you’ve had a terrible shock and are having difficulty in coming to terms with it.’

‘If anyone says “coming to terms” to me again, I think I’ll scream.’

I read through Greg’s emails so often that I almost knew them by heart. I thought they might give me a sense of his mood in the days and weeks leading up to his death. Was there a hint of anxiety? Anger? Apprehension? I couldn’t find anything and gradually they became familiar, like songs you’ve played so often you don’t hear them any more. Then I noticed something blindingly obvious, something that everybody in the developed world apart from me must already have known. Every email showed the exact time he had pressed the send button. Each email, whether from his home or his office computer, was a fairly accurate guide as to where Greg had been at a particular moment.

Within half an hour I was back from the stationer’s with two bulky carrier-bags. I tipped their contents on to the carpet. There was a large roll of poster-sized sheets of card, rulers, different-coloured pens and Magic Markers, highlighters, and sheets and sheets of little stickers – circles, squares and stars. It looked like the raw materials for a nursery-school art project.

I spread four of the cards in a row on the floor, using heavy books to hold the corners down. Then, using a ruler and a fine architect’s pen, I started to rule grids across them, each representing a week in the last month of Greg’s life. I traced seven columns, then drew horizontal lines cutting them into halves, then quarters, then eighths and so on, until I had chopped each column into a hundred and twenty rectangles, each representing ten minutes in a day starting at eight and finishing at midnight. I didn’t bother about the nights because we hadn’t spent a night apart in the last month.