In the distant future, man has not only started to settle on other planets and improved the transport system so that you can travel around the world (or to the moon) within hours. It has also become common to 'manufacture' human beings by chosing / manipulating genes that fit their intended purpose. You want the perfect soldier, agent, prostitute, broodmare? No problem at all, especially since those artificially created humans don't have human rights, so their owners can do with them as they please.
Friday is such a created woman. She's faster, stronger and more intelligent than normal people, which she needs for her job as a courier of secrets for a private company. While she spent the same abnormal childhood in a creche where she was treated as subhuman, she is now lucky because her boss and colleagues appreciate her and treat her like a person. She's extremely good at her job, too, and enjoys it despite - or maybe because of - its dangers. But then things start to go wrong badly: First she is caught and tortured by enemy agents, but can be saved. While on leave to recuperate, the family she married into finds out about her origins and drops her like a hot potato, and on her way back to headquarters she is suddenly cut off when a planet-wide series of terrorist attacks makes travel almost impossible and leads to aggression towards suspicious individuals such as her. In the end, she has to risk everything to save herself and the new friends she has found...
This is one of Heinlein's finest novels. It's full of suspense, adcenture, action and humour, while at the same developing a very convincing future world that can also give you quite a lot to think about. Add wonderfully well-developed and likeable characters, and this book is pure fun to read. I also find it amazing what a great female lead Heinlein put at the center of this book, a strong woman who is still womanly and very human. If you consider that this is a book written not only by a man but in the early 80s, that just shows how talented and original a writer Heinlein was. I'd say that if you don't already know Heinlein's books this is a very good place to start. It's also something that every SciFi-fan should enjoy.