The Tennis Party by Madeleine Wickham

It was Patrick's idea that they should have the tennis party. After all, he has the perfect setting -- the White House, bought out of his bonuses as an investment banker. He hasn't actually told Caroline, his brash and beautiful wife, what the real reason for the party is. She is glad to welcome Stephen and Annie, their impoverished former neighbours, less glad to see newly wealthy Charles and his aristocratic wife Cressida, and barely able to tolerate the deadly competitive Don and Valerie.

But as the first ball is served over the net it signals the start of two days of tempers, shocks, revelations, the arrival of an uninvited guest, and the realization that the weekend is about anything but tennis.