Mortimer has described her first novel, Maps of Our Spectacular Bodies, as "an elegy to my mum and to our relationship". Mortimer's mother died of cancer in 2010 and the book focuses on a fictional woman called Lia who has a "shapeshifting cancer inside her body. Moving between Lia’s past and present, the book is a look at memory, mother-daughter relationships, and coming to terms with death". Maps of Our Spectacular Bodies won the 2022 Desmond Elliott Prize, which is awarded for a debut novel published in the UK or Ireland. It was also shortlisted for the 2022 Goldsmiths Prize and longlisted for the 2022 Booker Prize.