It was at half past eleven exactly that the summons came. A petit bleu . Poirot tore it open, then handed it to me. It was from Madame Olivier, the world-famous scientist, whom we had visited yesterday in connection with the Halliday case. It asked us to come out to Passy at once.

We obeyed the summons without an instant’s delay. Madame Olivier received us in the same small salon. I was struck anew with the wonderful power of this woman, with her long nun’s face and burning eyes⁠—this brilliant successor of Becquerel and the Curies. She came to the point at once.

“Messieurs, you interviewed me yesterday about the disappearance of M. Halliday. I now learn that you returned to the house a second time, and asked to see my secretary, Inez Veroneau. She left the house with you, and has not returned here since.”

“Is that all, madame?”