ing's　guilt。　Bien　entendu；　that　was　not　the　original　idea。　The　te　de　la　Roche　was　to　be　the　scapegoat；　though　Ada　Mason　would　not　make　her　recognition　of　him　too　certain；　in　case　he　should　be　able　to　prove　an　alibi。　Now；　if　you　will　cast　your　mind　back　to　that　time；　you　will　remember　a　significant　thing　that　happened。　I　suggested　to　Ada　Mason　that　the　man　she　had　seen　was　not　the　te　de　la　Roche；　but　Derek　Kettering。　She　seemed　uncertain　at　the　time；　but　after　I　had　got　back　to　my　hotel　you　rang　me　up　and　told　me　that　she　had　e　to　you　and　said　that；　on　thinking　it　over；　she　was　now　quite　convinced　that　the　man　in　question　was　Mr　Kettering。　I　had　been　expecting　something　of　the　kind。　There　could　be　but　one　explanation　of　this　sudden　certainty　on　her　part。　After　my　leaving　your　hotel；　she　had　had　time　to　consult　with　somebody；　and　had　received　instructions　which　she　acted　upon。　Who　had　given　her　these　instructions？　Major　Knighton。　And　there　was　another　very　small　point；　which　might　mean　nothing　or　might　mean　a　great　deal。　In　casual　conversation　Knighton　had　talked　of　a　jewel　robbery　in　Yorkshire　in　a　house　where　he　was　staying。　Perhaps　a　mere　coincidence　…　perhaps　another　small　link　in　the　chain。〃

〃But　there　is　one　thing　I　do　not　understand；　Monsieur　Poirot。　I　guess　I　must　be　dense　or　I　would　have　seen　it　before　now。　Who　was　the　man　in　the　train　at　Paris？　Derek　Kettering　or　the　te　de　la　Roche？〃

〃That　is　the　simplicity　of　the　whole　thing。　There　was　no　man。　Ah　…　mille　tonnerres！　…　do　you　not　see　the　cleverness　of　it　all？　Whose　word　have　we　for　it　that　there　ever　was　a　man　there？　Only　Ada　Mason's。　And　we　believe　in　Ada　Mason　because　of　Knighton's　evidence　that　she　was　left　behind　in　Paris。〃

〃But　Ruth　herself　told　the　conductor　that　she　had　left　her　maid　b