Edinburgh basks in glorious, but brief, summer sunshine, and Isabel Dalhousie – philosopher, philanthropist and mother – searches for the perfect birthday present for her husband Jamie. While carefully seeking out a gift, Isabel finds herself at a viewing for an auction, and happens upon an old friend in distress – a friend who decides to unburden herself of her secrets, and to reveal a clue within a painting hanging on the walls of the auction house. Soon Isabel discovers that this secret binds her not only to her friend, but also to another woman. Questions about morality and loyalty disturb Isabel's peaceful existence with her young son and precious family, but she must face up to them in order to ensure that no-one is led astray.