Commander Dalgliesh investigates a horrible death at the Dupayne, a private museum on the edge of Hampstead Heath, dedicated to the years 1919-1939. One of the museum galleries displays exhibits from the most notorious murder cases of those inter-war years, and now a modern killer is at work, the crimes uncannily echoing the cases on display. All the people at the Dupayne - the trustees, the staff and the volunteers - have the means and the opportunity for murder. One of them has the ruthlessness to kill and kill again.