The Lost Art of Gratitude by Alexander McCall Smith.
I love the Isabel Dalhousie books! For those who are not familiar with her, Isabel is an Edinburgh-based philosopher (editor of The Review of Applied Ethics) with a toddler named Charlie, whose father is her much-younger paramour Jamie. Isabel also has a reputation for sleuthing, though there are those who call it interfering.
Early in this narrative, she runs into an old acquaintance, Minty Auchterlonie, who has a son about the same age as Charlie. Though Isabel has never thought of Minty as a friend, Charlie is invited to Minty's son's birthday party. Feeling that Charlie needs to be exposed to his peers, she accepts, only to find that Minty has an ulterior motive. Minty thinks that her son's father is trying to take him away from her, and asks Isabel to speak with him. Reluctanly, Isabel agrees, only to find that Minty hasn't told her the whole story.
Of course there are other plotlines in the book; her nemesis Professor Dove makes another attempt to oust her from the editorship of the Review, her niece Cat becomes engaged to a funambulist, and the fox who lives in her back garden is injured.
Although these books are definitely mysteries, they don't always include murders, which kind of refreshing. There is something gentle and charming about Isabel and her life, and it's a joy to read about.