Commonwealth by Ann Patchett

It is 1964: Bert Cousins shows up at Franny Keating’s christening party uninvited and notices a heart stoppingly beautiful woman. When he kisses Beverly Keating, his host’s wife, he sets in motion the joining of two families, whose shared fate will be defined on a day 7 years later. In 1988, Franny Keating, now 24, is working as a cocktail waitress in Chicago. When she meets the famous author Leon Posen one night at the bar, and tells him about her family, she unwittingly relinquishes control over their story.