In a telling nod, Mawer dedicates the book to the memory of Colette,
Anne-Marie Walters' field name, while Marian fends off the unwanted attention of an amorous suitor by insisting that her name is "Anne-Marie".
"She was obviously quite a lady," says Mawer of the real-life heroine. "She was quite sharp and maybe quite abrasive as a person, which maybe doesn't come across in her book but it does when you look at her S.O.E. file. Meeting her after the war would not have been an easy experience, as you wouldn't have understood the girl that she used to be before that.
"I saw her as a young girl, just out of school and a little bit impatient with life in Britain because she was born and brought up in Geneva and she knew French and English as an expatriate."
Having spent the last three decades living in Italy where he worked as a biology teacher at a boy's school in Rome, Mawer can sympathise with her situation as a perennial outsider. "I've taught children who are in that very position, who are half-Italian and half-English as well as many other nationalities.
"If you put that sort of background together with a certain independence of mind and spirit, you get somebody who has got some very definite ideas about things. I imagined Marian Sutro fetching up in Britain and finding it all just a little tiresome and slightly hankering after France. That probably happened to a lot of them. She can pretend to be either French or English under different circumstances but she is really neither one thing nor the other. My daughter is in exactly that position. Among Italians, she's Italian and among English, she's English."
Born in Oxford, Mawer admits that he doesn't know what to say when journalists ask what part of Britain he hails from, since his Air Force parents were constantly on the move when he was a child. "I kind of feel more English in Italy, as I often feel like a tourist in Britain. I'm a bit of a nomad but I've actually been very unnomadic since moving to Italy as we've now lived in the same place for more than 30 years."
Although his 1997 fifth book Mendel's Dwarf was long-listed for the Booker, Mawer was much a proverbial mid-list author until The Glass Room made the final cut for literature's most prestigious prize in 2009, the same year that it was also named best novel by the likes of the Observer and the Economist. But if the 53-year-old is having trouble adjusting to the demands of having penned a bestseller, he doesn't show it, although it might account for why The Girl Who Fell From The Sky is his most accessible and thrilling work to date.
"I wanted to make it [Marian's] story, starting with her recruitment," says Mawer, who jettisoned the shifting perspectives of his previous books for a more linear approach.
"That's just the momentum of the story because it all takes places in virtually three months, a month of her training and then a couple of months in France. I hope that the pace accelerates and becomes more breakneck as the book goes on, just as it would have been in real life. It's just like a rock rolling downhill and nothing else, just that one dimension, and that's why it turned into what it is. I enjoyed writing it. It's a grown-up adventure story."
Indeed Mawer is so beguiled by his enigmatic protagonist that he intends to return to her larger than life exploits in his next novel. "I'm currently working on a sequel, which I think will happen," he says. "I've never written a follow-up before but I really like Marian Sutro. She has left quite an impact on me."
The Girl Who Fell From The Sky (Hachette $36.99) is out now.