Mrs. Endicott's Splendid Adventure by Rhys Bowen

Ellie Endicott is stunned when her husband of 30 years tells her he wants a divorce to marry a “smart, pleasant,” much younger colleague. Once she has recovered from her shock and humiliation, she admits – to herself, at least – that she didn’t love him. As Ellie wonders what is next for her, Mavis, her cleaning lady, persuades her to consult a solicitor: