My father died just after I was born and I knew very little about him until I was in my 30s. I was a journalist then, and I approached it like an investigation, writing a memoir about what I discovered – his unhappy childhood, his life as a pilot in the navy, and his disappearance one November night during practice manoeuvres off the Dorset coast. The memoir was published in a book and serialised in a newspaper. After it appeared, my mother talked to me about him; not much but enough. She told me he had been a great love, and she told me in heart-rending detail about the night he didn’t come back. We both cried, which was good, because I had got used to thinking she had forgotten him. We had met for lunch, and when we had finished eating she rummaged in her shopper and brought out a plastic bundle, a small Ottakar’s bag containing a thick pile of letters. “You can read these,” she said. “If you like.”

I took the letters home, and I was going to read them that night. In some ways, it felt like victory. The teenage me, the one who in secret trawled for evidence, who had raged against her silence – would have drunk them in. I liked to think I had bypassed her in my search, because I hadn’t wanted to upset her. She was long remarried, with a life of her own. But if I am honest it had also been a way of snatching my father from her, of having him to myself. And maybe their letters were too much of a rebuke of this, provided too concrete a proof that he had been a lover, a husband, hardly a father at all. Or perhaps their existence was just too personal – that squeamish resistance all children feel towards parental intimacy. I put the Ottakar’s bag on the table in the hall, and at one point it was moved on top of the piano, and then it graduated into a space on the bookshelves behind. I stopped thinking about it. The bag, with its green logo and arc of orange, wasn’t sealed, the top with the handles just folded over, but it gave the impression of being bound in Sellotape and masking tape, of being as impenetrable as a cage.

Things have changed while the letters have sat there. I had two small children when my mother gave them to me, my third child is now 14. The Ottakar’s in Putney Exchange, where my mother bought her books, was taken over by Waterstone’s many years ago. And for the last 18 months my mother hasn’t shopped there anyway, because the summer before last she went to a wedding in Canada and when she came back she discovered she had cancer and two weeks later she died.

I’d always thought of death as something unusual, out of the ordinary, exceptionally unfair. Having a dead dad had made me interesting at school. Now, with the full force of my own mortality, I realise how ordinary death is. There’s nothing interesting at my age about having a dead parent. Lots of my friends are orphans, too. And the pain of it is very different. I had grown used to thinking of my father’s death as a hole, but now I realise it was a rock, a solid object, something you could rub up against. It’s the death of someone you have known and argued with and been frustrated by and loved – that’s a hole, that’s a crevice you have to stop yourself from falling down.

I used to collect objects that had belonged to my father – a paisley dressing gown, a hand-knitted jumper, a copy of Knots, Splices and Fancy Work, squirrel them away like talismans, proof he had existed. Faced with the onslaught of my mother’s effects, I could hardly bear to keep a thing. I wrestled her possessions into bags, manhandled them out of the house. Off you go. You’re not welcome here. I asked a friend to take away her little watch, get it out of my sight. But my friend cleaned it and wrapped it in tissue paper and brought it back; pressing it in my hand she said she thought I might regret not keeping it. And I knew she was probably right, but the truth of that felt a long way off.

Eighteen months have passed now and I am glad I have the watch. I wish I had more; not the clothes, perhaps, but the emails that disappeared, in a glitch with my server, and which I decided not to try to retrieve. I long to hear her voice, to have a bit of her back just for a moment. And as a result those old love letters have taken on a different force. I began to think again about reading them, circling the idea, like prodding a bruise – aware this time that it was more about her than him. I wouldn’t be reading them to discover, but to recover – to rewind time, to hear my mother’s words. She had given them to me. She had meant me to read them. And it began to feel like neglect, that I had somehow let her down.

Yesterday, I decided to pick them up at least, to feel the weight of them. But we had the decorators in last year and the bookshelf where I was expecting to find the solid package, between Jane Bown’s photographs and the RHS Book of Gardening, was just a neat row of hardback fiction. I went upstairs, to a room we call my study, where I would surely have put it for safe keeping. But it’s a bit of a mess at the moment, a teenage dumping ground, and I began hurling things out – clothes meant for Depop, and broken lamps – and with a growing sense of desperation, shouted: “Where’s the Ottakar’s bag?” And when my partner shouted back, “What Ottakar’s bag?” I felt an overwhelming sense of sickness and loss, remembering all the other precious things I had neglected – including my father’s old jumper and my mother’s emails – and when finally I did find it, carelessly thrown behind some photo albums, coated in builder’s dust, I was crying.

I didn’t know when I started writing this whether I would actually read them. I thought I would; that essay about my father was a way to control emotions that felt otherwise overwhelming. But there is the old resistance – a feeling that they are not mine to look at. The packet has been in front of me while I have been typing, heavier and more substantial than I remembered; a proper clout. I have begun to sigh a lot, those heavy tussles with breath that are an attempt to keep anguish at bay. But I am getting closer. Between that sentence and this I opened the bag and saw how each identical pale blue envelope has been neatly dated in my mother’s hand, that they span two years, 1961 and 62, the time before they were married, before I was born. There are 71 letters, and they were sent to different addresses – Brussels, Queen’s Gate, Copse Hill – all in the same spikey writing.

And it comes as a shock, this. I don’t know why I hadn’t realised it before, that they are not a correspondence. Her letters to him would have been received at base or at sea, on the move, read, perhaps kept for a bit, but ultimately discarded. These, cherished and dated and placed in this bag the morning she met me: they are all from him to her. Fifteen years ago it wouldn’t have mattered. But today there is an immediate ache of disappointment, that she isn’t to be found here after all.

A couple were loose, out of sequence, and I cast my eye over them. My dearest Anne (9 Jan 61), To my darling, darling Anne (Sept 62). The first was sent from HMS Victorious and is full of boyish high spirits: “There is a gale blowing at present so flying has been rather tricky as the flight deck moves round rather a lot making landing very difficult.” The second, written at Hal Far, is full of longing. “I’m too miserable here without you to write very much.” It’s enough. The poignancy is too painful in view of what was to come.

I slip the letters back into the bag and I lay it at my feet. I think about her taking the letters from wherever it was she kept them (not her desk); and the love in her decision to give them to me. Was it by her bed, that bookshop bag? Had she just bought herself a novel? I think about how much she liked Ottakar’s in Putney, the layout, and the nice Costa on the second floor, where she would order an Americano, and her tendency to chide the shop assistant, if I didn’t get there in time, for not prominently displaying my books.

And I remember the expression on her face when she gave me the letters. She had a habit, my mother, of showing you her holiday photographs while holding them in such a firm grip you had to strain your neck to see – quite often I experienced entire cruises upside down. And that’s what I think of when I remember this handing over. She was still holding tightly to the bag, not really letting go, even when they were already in my hand.

Take Me In, by Sabine Durrant, is published on 28 June by Mulholland, at £12.99. Buy it for £11.04 at guardianbookshop.com