It would have been from the 1950s and featured a female agent(?) working outside the law, mostly, a bit like Simon Templar.
She had a trusty male sidekick of course and he made a telescopic bow that she used to kill her opponents silently. One of her favourite ploys was to pop up bare-breasted and shoot them while they were distracted.
I am quite sure that is the right answer. As a teen reader I would never forget the bare-breasted trickery. Here’s a bit more about her skills: The magnificent Modesty Blaise
On weaponry Fleming is outclassed by O’Donnell, I think, because both Modesty and Willie Garvin are expert in every kind of combat invented by humans, and probably some that O’Donnell invented himself. We hear a lot about throwing knives and a special kind of throwing and bashing weapon that lurks in the back of Modesty’s hairdo. O’Donnell is really good on ingenious places for hiding weapons: time and again Modesty strips off her clothes so she can extract the components of a bomb, or a radio transmitter, or a bow and arrows, from her underwear or her skirt. They’re kept in the seams and under false linings. It’s a good thing airport scanners hadn’t been invented then.
OK, well, my book reads at though it’s a Nick Hornby book. It’s about this guy who kind of has a crush on a celebrity. Her “candid” photos get leaked and he, uh, likes her even more. Then, somehow, they end up meeting and dating for a while.
I remember it being a fun, funny book to read, again in the style of a Nick Hornby book, but I can’t remember the title or author.