The Quiet Side of Passion by Alexander McCall Smith
Isabel finds herself befriended by Patricia, a single mother whose son, Basil, goes to school with Isabel's son. Isabel discovers that Basil is the product of an affair Patricia had with a well-known Edinburgh organist, also named Basil, who was, rumor has it, initially reluctant to contribute financially to the child's upkeep. Though Isabel doesn't really like Patricia, she tries to be civil and supportive, but when she sees Patricia in the company of an unscrupulous man who may be a wanted criminal, her suspicions are aroused and she begins to investigate the paternity of Basil Jr.
When Isabel takes her suspicions to Basil Sr., she finds that, although he is paying child support and wishes he could have more of a relationship with Basil Jr., Patricia has no interest in Basil Sr. taking a more hands-on role in Basil Jr.'s parenting, even as she continues to accept his financial support. Should Isabel help someone who doesn't want to be helped?
As Isabel navigates this ethically-complex situation, she is also dealing with her niece, Cat, who has taken up with a brawny and opinionated tattoo shop clerk? Isabel considers herself open-minded, but has Cat pushed it too far this time? As ever, Isabel must use her kindness and keen intelligence to determine the right course of action.
In this twelfth full-length installment of Isabel's story, McCall Smith gives his readers what we want--time inside the mind of one of fiction's most richly developed women detectives, a visit to Edinburgh, and a twisting and tangled mystery about what responsibility humans owe to each other.