The premise is that it's 1943, and the agent, Queenie, has been captured. The Gestapo have been torturing her (rather more torture description than I prefer to read in general, but I never felt that it tipped over into being gratuitous or self-indulgent) - and she's writing down everything she knows about the British War Effort.
For some reason, she is writing it in the form of a story told from the point of view of the female pilot who flew her to France. Queenie is an aristocratic scion of an old Scottish family, the pilot is heir to modest wealth from the new motor cycle industry, and the story is really about how they have become friends.
I hit the first 'hang on, that's not right' thing on page 10, and I confess that I did think 'bloody American writers' at first, because it seemed like a failure in the local 'tone' research. But I went on reading, and kept hitting 'hang on, that's not right' - and it quickly became clear that in fact Queenie was lying. She was telling a story peppered with lies, with just enough local description to give it an air of vague likelihood to someone not English.
I thought this was brilliant! What a wonderful game! So I went on reading, absolutely captured by the premise - on the one hand, it was an entertainingly told story, and on the other hand, clearly there was a whopping great complicated lie happening, and I was trying to spot it. Trying to work out if it was possible to spot the real story behind the lie, and desperately cudgelling my brain for half-forgotten names of airfields and so on. Compelling stuff. Bit like a whodunnit.
Then I got to the end of the half of the book that is Queenie's Scheherazade story for the Gestapo - and there is a lovely spice added by the fact that the Gestapo officer in charge calls her Scheherazade, and is clearly aware that she is tale-telling to spin out her own life. He knows what is going on, or some of it - but how much? Has he caught the details I caught? And there are faint flickers that the guard, Engel might not be all she seems either...
At that point, you will remember, the story swaps to being told by Maddie, the pilot, who is undercover and being looked after by the Resistance (I did get faint echos of 'Allo, 'Allo' at this point, but I tried really hard to ignore them, because the book seemed too good to allow the ghost of Herr Flick to intrude, although I admit I probably did imagine the Gestapo woman guard Engel as Helga.)
Anyway, at this point I started to get a little confused. Because Maddie, who is now telling the tale - is NOT supposed to be lying. Maddie is telling the straight truth about her situation. And yet, Maddie also uses the names of airfields that never existed, that are clearly fabrications. Is Maddie lying too? Is this another twist? I read on fervently, trying to solve the puzzle. Surely Maddie can't possibly *really* be writing down all this highly confidential material in plaintext while still living under cover with people who would all die if her diary was found? Careless talk costs lives, she knows that, and yet, here she is naming names, giving places, times, descriptions of people. There must be something else going on!
And then I got to the end of the book and the Resistance tried to rescue Queenie, failed, and Maddie had to shoot Queenie to save her from a terrible fate as a human experiment subject in a concentration camp. (They did blow up the Gestapo headquarters, which was satisfying). And it turned out there was no great puzzle to solve after all: although I was right that Queenie had been lying in her story, the author had just made up the airfield names as 'an easy way to avoid historical incongruity' according to her afterword.
And there is no explanation at all about why Maddie, who generally seems a sensible and competent woman, would be so utterly irresponsible and pigheadedly stupid as to keep a written diary full of helpful details that would certainly condemn not only herself, but her best friend and her brother and all the people trying to help her if it were found. That seemed very out of character.
So for most of the book, I think I was actually reading a book that was not entirely the book the author wrote.
It was a bloody good book though.