The Story of San Michele (a villa built on the ruins of a Roman Emperor's villa in Capri) is a series of overlapping vignettes, roughly but not entirely in chronological order. It contains reminiscences of many periods of the author's life. He associated with a number of celebrities of his times, including Jean-Martin Charcot, Louis Pasteur, Henry James, and Guy de Maupassant, all of whom figure in the book. He also associated with the very poorest of people, including Italian immigrants in Paris and plague victims in Naples, as well as rural people such as the residents of Capri, and the Nordic Lapplanders. He was an unabashed animal lover, and animals figure prominently in several stories, perhaps most notably his alcoholic pet baboon, Billy.
The stories cover a wide range in terms of both how serious they are and how literal. Several discussions with animals and various supernatural beings take place, and the final chapter actually takes place after Munthe has died and includes his discussions with Saint Peter at the gates of Heaven. At no point does Munthe seem to take himself particularly seriously, but some of the things he discusses are very serious, such as his descriptions of rabies research in Paris, including euthanasia of human patients, and a suicide attempt by a man convinced he had been exposed to the disease.
Several of the most prominent figures in Munthe's life are not mentioned in Story of San Michele. His wife and children do not figure in the narrative; very little of his time in England is mentioned, even though he married a British woman, his children were largely raised in England, and he himself became a British citizen during the First World War. His decades-long service as personal physician and confidante to the Queen of Sweden is mentioned only in the most oblique terms; at one point, while naming her only as "she who must be mother to a whole nation", he mentions that she regularly brings flowers for the grave of one of her dogs buried at Villa San Michele, at another point, one of his servants is out walking his dogs, and encounters the Queen, who mentions having given the dog to Munthe.
Munthe published a few other reminiscences and essays during the course of his life, and some of them were incorporated into The Story of San Michele, which vastly overshadows all his other writing both in length and popularity. Notably, his accounts of working with a French ambulance corps during the First World War are not included.
World wide, the book was immensely successful; by 1930, there had been twelve editions of the English version alone, and Munthe added a second preface. A third preface was written in 1936 for an illustrated edition