Another of John D. MacDonald's infidelity novels, and like the other two, Cancel All Our Vows and The Deceivers, this one is excellent.
The book's milieu is classic Updike/Cheever country. A happily married suburban businessman is left alone for the summer, his English wife bringing their children back to the home country to meet relatives. He meets a young Bohemian girl who lives in a loft in the city (and off of a trust fund). There's lots of drinking and lots of sex and things turn sour a la Fatal Attraction. It's a long book but doesn't feel it. JDM manages to turn this crime-free tale into a tale of high suspense. It's dated, of course, in its free-wheeling attitudes toward extra-marital activity, and it's almost comical the number of times the main character gets behind the wheel completely sloshed, but, ultimately, it's a heartfelt well-written novel without gimmickry.