n 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 behind there；〃 demurred Van Aldin。
〃Ah！ I am ing to that。 We have Mrs Kettering's own evidence there； but； on the other hand； we have not really got her evidence； because； Monsieur Van Aldin； a dead woman cannot give evidence。 It is not her evidence； but the evidence of the conductor of the train … a very different affair altogether。〃
〃So you think the man was lying？〃
〃No； no； not at all。 He spoke what he thought to be the truth。 But the woman who told him that she had left her maid in Paris was not Mrs Kettering。〃
Van Aldin stared at him。
〃Monsieur Van Aldin； Ruth Kettering was dead before the train arrived at the Gare de Lyon。 It was Ada Mason； dressed in her mistress's very distinctive clothing； who purchased a dinner basket and who made that very necessary statement to the conductor。〃
〃Impossible！〃
〃No； no； Monsieur Van Aldin； not impos