Fantasy has lots of sex workers or courtesans who also work as spies — but for our money, the best is Phèdre nó Delaunay de Montrève, the hero of the first Kushiel trilogy by Jacqueline Carey. She thwarts a major conspiracy, stops an invasion, saves her country and avenges her master... with kinky sex.
Seriously, if you haven't read Kushiel's Dart, it's a great weekend read. I won't spoil it too much here — but suffice to say it takes place in an alternate world where Jesus had a bastard son named Elua, who started a religion of pure love. And one of Elua's main acolytes was Naamah, who's basically the patron saint of sex workers. And in this alternate late medieval France, instead of Christianity, everybody worships Elua and Naamah. (Except for the Jews, who worship Jesus. It's wacky.)
Into this sex-positive alternate Earth is born Phèdre, who's left by her mother to be trained as a courtesan... but she's different from all the other boys and girls. Because she's an anguissette, who can turn pain into pleasure. That's like her super-power. She's a super-masochist. (Not like Bob Flanagan.) And then Phèdre gets acquired by a mysterious nobleman named Lord Delaunay... who doesn't want her for his own pleasure. (He's gay.) But instead, he wants to use her rare ability to please a certain type of nobleman to find out information. Delaunay trains her to be not just the perfect courtesan, but to use her vulnerability to gain the confidence of these powerful men and women, so they betray their secrets to her. So she gets hired by sadistic nobles, and in the process begins uncovering the hints of a conspiracy to take over her alternate France, known as Terre D'Ange.
It's a rollicking great adventure, and not quite as perverted as that thumbnail sketch makes it sound — the sex is very much integrated into the culture and the alternate religion, and eventually the practice of magic. And Phèdre is an amazing protagonist, who's resourceful and clever and raunchy and subtle and surprisingly compassionate for someone who doesn't fear pain. If you want to read about a spy who never wears a tuxedo or uses a pen-laser (and who doesn't meet the same fate as a lot of other sex-worker spies), then these books are massively recommended.