<p> Framed in the doorway of Hercule Poirot?s bedroom stands an uninvited guest, coated from head to foot in dust. The man stares for a moment, then he sways and falls. </p> <p> Who is he? Is he suffering from shock or just exhaustion? Above all, what is the significance of the figure 4, scribbled over and over again on a sheet of paper? Poirot finds himself plunged into a world of international intrigue, risking his life?and that of his ?twin brother??to uncover the truth. </p>