For those unfamiliar, probably the easiest way to describe Modesty Blaise is as a sort of female James Bond. It's not an entirely accurate description, but it does give the basic idea.
Like Bond, this first Modesty book was written in the mid-Sixties, and that sometimes causes more cognitive dissonance than if it were set far longer ago, because the society depicted is enough like the present to seem familiar but different enough to jar quite badly at times, especially in the way everybody smokes incessantly and in the attitudes toward women. Although Modesty herself is a strong and independent character, the men around her don't always recognise that.
If you can cope with that and the sometimes unnecessarily detailed descriptions of clothes and furniture, there's a pretty good adventure story in there. Modesty has retired from a life of running an extensive criminal network and is now living respectably in England. So when Sir Gerald Tarrant approaches her to do a job for the British Government, she is reluctant - until he reveals to her that her former sidekick and friend Willie Garvin is in great danger and gives her the information she needs to save him. Things get more complicated from then on and there are fights and snappy dialogue and plots and counterplots. Great fun for the most part.
