The book I am currently reading Mark Vernon’s Dante’s Divine Comedy: A Guide for the Spiritual Journey. It’s partly an introduction to the epic and fantastic journey Dante undertakes, but more importantly it’s about reading The Divine Comedy as a way to change your own consciousness. There are insights on every page. The book that changed my life All sorts of books throughout my life have nudged me this way and that – like winds in a sail, I suppose. I hope they continue to do so. From Charles Palliser’s The Quincunx I learned that you didn’t have to write a 21st-century novel if you didn’t want to; you could write a 19th-century one. From Neil Gaiman’s The Sandman I learned to be courageous in writing. This question also works the other way round: my life keeps changing books. Jane Austen’s Emma is quite different today from when I read it first as a teenager. The book I wish I’d written The Man Who Was Thursday by GK Chesterton. It’s an extraordinary novel, funny and clever. It is subtitled A Nightmare. But it’s an odd sort of nightmare – one where terror keeps dissolving into cheerfulness (which is the opposite way round from most nightmares, and from a lot of contemporary fiction). Chesterton describes scenes and objects and colours with an almost heraldic vividness – or, looked at another way, as if they were pages in a modern graphic novel. He makes London feel like a fairytale, which to him I think it was. I have read The Man Who Was Thursday many, many times, but I still don’t understand it. I’ll keep going. A word of warning: it is a book of its times. There are no women characters. Well, there might be one, but she says three things and vanishes immediately. The book that had the greatest influence on my writing Probably CS Lewis’s Narnia series. Or possibly Ursula K Le Guin’s Earthsea (the original trilogy). In the end it is impossible to get this down to a single book: apart from anything else, I suspect that the strongest influences are probably not conscious. After I had finished writing Piranesi I reread Jorge Luis Borges’s short story “The House of Asterion”, which I hadn’t read since my 20s and which contains a labyrinth. I thought that there would be a connection between them, but I was stunned to find all these details in the Borges story which I’d no memory of but which had echoes in Piranesi. The book I think is most underrated Till We Have Faces by Lewis. It is a retelling of the Psyche and Cupid myth, set in a barbaric country contemporary with Classical Greece. One of the things it is about is the friction between those who have faith and those who don’t. The book has an unusual generosity in that it takes both sides seriously. The kindest, noblest character is a Greek philosopher and atheist. It’s as if Lewis made a portrait of his fiercest critics and said: “This is a good and admirable man.” The book I couldn’t finish The White Hotel by DM Thomas. It is an extraordinary book and caused a great sensation when it was published in the 1980s. I remember reading it on a train. I was getting towards the end and in the midst of a description of a massacre of Jews in Ukraine during the second world war the train pulled into Nottingham station and I had to get off. Afterwards I lacked the courage to go back to the horror of Babi Yar and so I never actually finished the book. Not a fault in the book, a fault in me. The last book that made me cry The Book of Margery Kempe. The part where Margery (the first woman to write her autobiography in English) goes to meet Julian of Norwich (the first woman to write any sort of book in English). Margery was a rather anguished person, constantly wondering which of her many and varied impulses came from the devil. Julian’s response to her is full of encouragement and Margery’s admiration of Julian shines through. A meeting between two extraordinary women in the 15th century and we have an account of it. The last book that made me laugh Probably Neil Gaiman’s The Graveyard Book. Sad and funny all at once. The book I’m ashamed not to have read I’m not fond of the idea that there is a list somewhere of books that you “ought” to read. There are too many “oughts” already. Read the books that help you flourish, that enlarge your world. Your books are bound to be different from other people’s. For myself I would like to be enlarged by reading more poetry and finding a way into Dostoevsky. The book I give as a gift I try to give books that I think the person will like. I gave Richard Osman’s The Thursday Murder Club as a Christmas present to my husband because he loves detective stories and he loves Richard Osman. But, as my husband knows, the same is also true of me. So on Christmas Day we solemnly exchanged copies of The Thursday Murder Club. My earliest reading memory I remember being taken to a library and being allowed to choose a book. I chose one of Alison Uttley’s Little Grey Rabbit books. Then we went home and I took my coat off and read the book. When I finished I imagined we would immediately go back to the library to get another one. But apparently that’s not how it works. I had to wait a whole week. A whole week. My comfort read When I was in hospital five years ago, I pretty much reread all of Diana Wynne Jones’s books. I love her take on how magic works, I love her characters, I love her stories. I love pretty much everything about her. Susanna Clarke’s Piranesi (Bloomsbury, £14.99) is shortlisted for the Women’s prize. To support the Guardian and the Observer buy a copy at guardianbookshop.com. Delivery charges may apply.