A ruthless international cartel seeks world domination... Framed in the doorway of Poirot's bedroom stood an uninvited guest coated from head to foot in dust. The man's gaunt face stared for a moment then he swayed & fell. Who was he? Was he suffering from shock or just exhaustion? Above all what was the significance of the figure 4 scribbled over & over again on a sheet of paper? Poirot finds himself plunged into a world of international intrigue risking his life to uncover the truth about ' Number Four'.