He came to an abrupt pause, as his eye was caught by the key of the desk itself, to which a dirty envelope was affixed. Poirot frowned at it and withdrew it from the lock. On it were scrawled the words: “Key of Roll Top Desk,” in a crabbed handwriting, quite unlike the neat superscriptions on the other keys.

“An alien note,” said Poirot, frowning. “I could swear that here we have no longer the personality of Mr. Marsh. But who else has been in the house? Only Miss Marsh, and she, if I mistake not, is also a young lady of method and order.”

Baker came in answer to the bell.

“Will you fetch madame your wife, and answer a few questions?”

Baker departed, and in a few moments returned with Mrs. Baker, wiping her hands on her apron and beaming all over her face.