The Sweet Dove Died by Barbara Pym
A chance encounter over a Victorian flower book brings together Humphrey, an antiques dealer, his nephew James, and Leonora. Although she is considerably older, Leonora develops a fondness for James all the while knowing Humphrey has feelings for her. Leonora is determined to keep James under her spell until she realizes that she has to contend with the bookish Phoebe. Then Ned, a wicked young American, appears on the scene.