When Doris Lessing was eight she was sent to a convent school where the nuns stopped her reading the classics. They thought Walter Scott, Robert Louis Stevenson and Rudyard Kipling unsuitable for a girl her age. Though many children would have been cowed by this stipulation, Lessing was undeterred. She wrote to her parents, asking them to tell the nuns she had their permission. As she later explained in her autobiography, “What was my own, where I belonged, was the world of books, but I had to fight for it.”

Four months after Lessing’s death in November 2013, I was asked to come to her house in West Hampstead, London, because the executors of her estate had a problem. Her house contained more than 4,000 books that had to be inventoried in order for the estate to be settled. I agreed to help – I wanted to know what sort of reader Lessing had been, whether she folded page corners, highlighted passages, wrote in the margins or on blank pages. I thought that learning what she read, and how, would shed light on her work.

On my first visit I was given a tour by Anna, who had been Lessing’s physical therapist. Almost every wall had a bookcase on it, and there were piles of books on the floor. On the third floor Anna unlocked a door. “These are all books by Doris,” she said. We were silent for a moment, looking at the sagging shelves that ran along two walls and down half of a third, the piles of books on a table, a desk and all over the floor. It was the overflowing accumulation of a 60-year career.

In addition to cataloguing the books, I had to identify those that might be of interest to Lessing’s future biographer (Patrick French was appointed the following year). I had to check their pages for notes or places where Lessing had marked the text. She probably would not have approved of me looking through her books for biographical crumbs. She cast doubt on the need for any novelist to have a biographer, arguing that anyone “can tell from a novel, let alone two or several, most things about a writer”.

Eastern religions and magic books … an expanding universe of posibilities. Photograph: Nick Holdstock

For the record, Lessing was born Doris May Tayler in 1919 in Kermanshah, Persia (now Iran). When she was five, her family moved to Southern Rhodesia (now Zimbabwe). At 19 she married Frank Wisdom, with whom she had two children, John and Jean. In 1945 she left them and married Gottfried Lessing, whom she divorced in 1949. In that year, she came to England with the manuscript of her first novel, The Grass Is Singing, and her son Peter, the only child of her second marriage. The publication of The Golden Notebook in 1962, an exploration of generational conflict, gender politics and mental illness, brought her international fame. In 2007 she was awarded the Nobel prize for literature. She didn’t know she had won until she was besieged by reporters outside her home. “Oh, Christ,” was her reaction.

I wanted to know what sort of reader she had been, if she folded page corners, highlighted passages, wrote in margins

The French writer Georges Perec proposed that “every book collection corresponds to two needs that are also often obsessions: the need to hang on to things (books) and the need to keep them in some order”. But Lessing’s library seemed untouched by what Walter Benjamin called “the mild boredom of order”. RSPB Birdfeeder Garden was next to Islam in Britain 1558-1685 and Barbara Kingsolver’s novel The Poisonwood Bible. Even the shelves near the kitchen had more than just cookery books. Elizabethan Country House Cooking was next to The Somme: An Eyewitness History and Second Sentence: Inside the Albanian Gulag.

It wasn’t only order that was lacking. During my first week I found little trace of Lessing as a reader. No page corners were folded, there were no notes or passages underlined. She hadn’t even written her name inside the books. By the end of my second week I regretted taking on the job. The joints of my fingers were swollen from recording bibliographic information. I started taking breaks on the small patio outside the kitchen. From there I could look down into the long garden that ended in two trees. Birdfeeders hung from many branches; cats often patrolled. It was a tranquil spot where Lessing must have sat, enjoying birdsong and the hum of bees.

My dwindling motivation wasn’t the only interruption. Lessing’s daughter Jean was visiting from South Africa, and wanted time alone in the house. She was also curious to meet the total stranger who had been entrusted with her mother’s books. We sat in the lounge and she asked me precisely, though not unkindly, about the work I was doing. She seemed satisfied by my answers, and we moved on to talking about her life in Cape Town. But I felt I should have been able to produce a pile of books that bore an indelible trace of her mother. I wanted to be able to say: “Here is a book she loved.”

I found 19 copies of Lessing’s Nobel prize acceptance speech in a box under the bath

It took another two weeks before I found them. On a high shelf in the lounge there was a row of squat hardbacks, bound in faded green or orange cloth, from the Everyman’s Library series. There was Sophocles, Homer, Plato, Ibsen and Stendhal, inside which were stickers from bookshops in Salisbury (now Harare), Rhodesia. Later in life, Lessing would recall the experience of opening “the parcels with a beating heart, longing for the newer shores of literature”. When she first came to London she brought some of them in “a couple of trunkfuls … for I would not be parted from them”.

On the same shelves were books that friends and family had given her. In a copy of Thomas Mann Presents the Living Thoughts of Schopenhauer, given to her for Christmas in 1952, her son John had written: “The gospel of gloom on the feast of love.” In The House at Pooh Corner, Peter had written in blue pencil: “Mummy is 40.” But most of the messages in the books were from other writers. There were dedications from Raymond Carver, Kurt Vonnegut, Brian Aldiss, Allen Ginsberg, Alberto Manguel, Christopher Logue, Robert Anton Wilson, Penelope Mortimer, Naomi Mitchison, Alan Sillitoe, Betty Friedan, Colin Wilson and Muriel Spark, a testament to the breadth of Lessing’s literary influence.

Slowly, shelf by shelf, I progressed. I found 19 copies of Lessing’s Nobel prize acceptance speech in a box under the bath. In it she spoke of the power of the storytelling impulse, and the need for books to be available in rural communities. “Writing, writers, do not come out of houses without books.”

Answers to questions … Doris Lessing’s collection of pamphlets. Photograph: Nick Holdstock

Most people’s bookshelves have a few volumes that don’t seem to fit: a John Grisham thriller tucked between Proust and Dickens, a book about Norman churches on a shelf of Mills & Boon. On Lessing’s shelves, the aberrations were The New Soviet Psychic Discoveries, The Cat in the Mysteries of Religion and Magic and Is This Your Day? How Biorhythm Helps You Determine Your Life Cycles. There were books about Atlantis, UFOs, ESP, the hidden powers latent in our bodies. This interest in the paranormal and pseudoscience suggests that Lessing was searching for alternative ways to explain human behaviour. In her autobiography she admits to being frequently baffled about her own motivations, especially her involvement in communism in her 20s and 30s. As JM Coetzee wrote in his review of these books: “With the best will in the world, she cannot get to the bottom of why she did what she did.”

Part of the attraction of ideas like ESP and cosmic waves is that they expand our notion of what’s possible. Like fiction, they hold the promise of transcending physical and mental limitations, of becoming someone different. Yet Lessing often expressed a view of human character that denied the apparent freedom offered by such ideas. She repeatedly denied the possibility of agency in her life, asking: “What is the use of ever saying, I should have done this, should have done that? The point was, nothing else could have happened given my nature and circumstances.”

Part of the attraction of ideas like ESP and cosmic waves is that they expand our notion of what’s possible

It was only in the last room, at the top of the house, that I found books that answered such questions. This small converted roof space was Lessing’s bedroom and office. From the balcony she could look south-east to the Houses of Parliament, but it was so quiet here that she sometimes recalled her African childhood. She once wrote that “down the hill a cock sometimes crows and at once I hardly know where I am”.

Amid the chaos of the room there was a small white bookcase holding around 100 books and pamphlets that clearly belonged together. These were about Sufism, which Lessing first encountered at the end of the 1950s. She described it as “a main current” in her life, one “deeper than any other, my real preoccupation”. According to Jenny Diski, who lived with Lessing as a teenager, Sufism “seemed to lock all her former passions together, neat and tight as a Rubik’s cube”.

Among these books I finally found one containing Lessing’s responses to the text. In The Teachers of Gurdjieff by Rafael Lefort many passages were underlined, often so unevenly that the words were crossed out. The comments suggested a degree of readerly enthusiasm. Lessing’s response to the sentence “You have no time to waste on academic research or intellectual evaluation of half-truths” was an emphatic “Yes!” By another passage she had written: “I know nothing but this.” Best of all, Lessing had drawn faces next to several passages. They wore hats and had particular expressions. The eyes in the face drawn next to the tautological statement “It is not hidden knowledge but useless knowledge unless you have the capacity to use it”, were looking sideways at the text, perhaps doubtfully. No such equivocation was on the face drawn next to the sentence “You start by mastering the ability to learn”. It was smiling, its hat jauntily perched.

Battered grey beast … Doris Lessing’s typewriter. Photograph: Nick Holdstock

After the white bookcase, all that was left was a short row of books on Lessing’s desk. Much of the space was taken up by her battered grey typewriter. There was a box of pens and a note on it like a Zen koan: “Pens generally don’t work but some do.” The books were mostly for reference. There were two thesauruses, a Bible with bookmarks in Job and Ecclesiastes, a Shorter Oxford English Dictionary, an atlas, a Penguin Chronology of the Modern World that had split into two parts, an Everyman’s Dictionary of Non-Classical Mythology, a Chambers Biographical Dictionary from 1911 that claimed to contain “The Great of All Times and Nations”, a decrepit copy of Steingass’s Persian-English Dictionary, and a copy of Fowler’s Modern English Usage she had owned since 1937.

The final item I catalogued was a pamphlet called Mummies, on the cover of which the Egyptian god Anubis was pulling on a set of balance scales while being observed by a mouse-like creature. On the cover, her son Peter had written: “Doris – see plate 2.” When I found the plate, it was of a portrait that had been painted on the head of a mummy. I could see a slight resemblance to Lessing, enough to think that Peter might have too. If this wasn’t some sweet visual joke, why else had this pamphlet sat on Lessing’s desk for decades?

Each book had played a role in shaping the mind and work of Lessing, but they weren’t a record of her thoughts

This was an appealing notion, but perhaps completely wrong. Peter could just as easily have thought the woman resembled someone he and his mother knew. In many ways the problem was the same as with all the other books: each had played a role in shaping the mind and work of Lessing, and so had to be of some interest. But they weren’t a record of her thoughts. The books were personal and they mattered. But they weren’t pieces of her.

Lessing once wrote: “Every novel is a story, but a life isn’t one, more of a sprawl of incidents.” But while it’s true that most lives (Lessing’s included) are far messier than anything found in fiction, some events are neat enough to seem written. Several months after I’d finished cataloguing, the fate of Lessing’s library was announced. While some books would go to a special collection at the University of East Anglia, the majority were sent to the public library in Harare. Judging by her Nobel speech, Lessing would have approved. She’d have hoped they might do what the classics had done for a young girl called Doris, who just wanted to read.