Three Act Tragedy : Hercule Poirot #11

Thirteen guests arrive for dinner at the house of Sir Charles Cartwright, the famous actor. To avoid bad luck, his secretary insists on making up the number to fourteen, bit its too late for one guest, who chokes to death on his apéritif...But when his martini glass was sent for chemical analysis, there is no trace of poison - just as Poirot had predicted. What causes the famous detective greater anxiety, however, is the complete lack of any motive.