In London, a crazed individual is breaking into art galleries and private homes to slash valuable paintings of women, and Scotland Yard is at a loss. When Joanna and the Watsons are called in to solve the mystery—their fourth, on the heels of The Disappearance of Alastair Ainsworth—they conclude that the slasher is searching for something hidden behind the portraits. After two suspects are killed, Joanna forms a plan for ensnaring the criminal before more lives are lost.