Many years ago I tried valiantly but just could never finish a Le Carre “thriller”. According to his reasoning Mata Hari was not a spy, but Edith Clavell was. Guess what John they both were.
The only other book that came close to turning me off as much was Dutch the official biography of Ronald Reagan, although for very different reasons. In that book the nitwit author inserted his own character in the story of Reagan's life and seemed to give more attention to the fictitious character than to the true exploits of Reagan himself. In a biography? I don't think so!
Mata Hari, was an adventuress, for lack of a better word. She may well have been a spy, though there is some doubt. If she did do it, it was not from any sense of conviction, but for money or she was using or being used by her lovers.