The Comfort of Saturdays by Alexander McCall Smith

Isabel Dalhousie is a new mother and a connoisseur of philosophy; she'd rather not be a sleuth. But when a chance conversation at a dinner party draws her into the case of a doctor whose career has been ruined, she cannot ignore what may be a miscarriage of justice. Because for Isabel ethics are not theoretical at all, but an everyday matter of life and death.
As she attempts to unravel the truth behind Dr Thompson's disgrace, Isabel's patient intelligence is also required to deal with challenges in her own life. There is her baby son Charlie; Cat's deli to look after, not to mention her vulnerable assistant Eddie; and a mysterious and unlikeable composer who has latched on to Jamie, making Isabel fear for the future of her new family.
Isabel treads a difficult path between trust and gullibility, philanthropy and interference, while keeping in her sights the small but certain comforts of family, philosophy and a fine Saturday morning.