“This Big Four, they make me to bestir myself, mon ami. I run up and down, all over the ground, like our old friend ‘the human foxhound.’ ”
“Perhaps you’ll meet him in Paris,” I said, knowing that he referred to a certain Giraud, one of the most trusted detectives of the Sûreté, whom he had met on a previous occasion.
Poirot made a grimace. “I devoutly hope not. He loved me not, that one.”
“Won’t it be a very difficult task?” I asked. “To find out what an unknown Englishman did on an evening two months ago?”
“Very difficult, mon ami. But as you know well, difficulties rejoice the heart of Hercule Poirot.”
“You think the Big Four kidnapped him?”
Poirot nodded.
Our inquiries necessarily went over old ground, and we learnt little to add to what Mrs. Halliday had already told us. Poirot had a lengthy interview with Professor Bourgoneau, during which he sought to elicit whether Halliday had mentioned any plan of his own for the evening, but we drew a complete blank.
Our next source of information was the famous Madame Olivier. I was quite excited as we mounted the steps of her villa at Passy. It has always seemed to me extraordinary that a woman should go so far in the scientific world. I should have thought a purely masculine brain was needed for such work.
The door was opened by a young lad of seventeen or thereabouts, who reminded me vaguely of an acolyte, so ritualistic was his manner. Poirot had taken the trouble to arrange our interview beforehand, as he knew Madame Olivier never received anyone without an appointment, being immersed in research work most of the day.
We were shown into a small salon, and presently the mistress of the house came to us there. Madame Olivier was a very tall woman, her tallness accentuated by the long white overall she wore, and a coif like a nun’s that shrouded her head. She had a long pale face, and wonderful dark eyes that burnt with a light almost fanatical. She looked more like a priestess of old than a modern Frenchwoman. One cheek was disfigured by a scar, and I remembered that her husband and coworker had been killed in an explosion in the laboratory three years before, and that she herself had been terribly burned. Ever since then she had shut herself away from the world, and plunged with fiery energy into the work of scientific research. She received us with cold politeness.
“I have been interviewed by the police many times, messieurs. I think it hardly likely that I can help you, since I have not been able to help them.”
“Madame, it is possible that I shall not ask you quite the same questions. To begin with, of what did you talk together, you and M. Halliday?”
She looked a trifle surprised.
“But of his work! His work—and also mine.”
“Did he mention to you the theories he had embodied recently in his paper read before the British Association?”
“Certainly he did. It was chiefly of those we spoke.”
“His ideas were somewhat fantastic, were they not?” asked Poirot carelessly.
“Some people have thought so. I do not agree.”
“You consider them practicable?”
“Perfectly practicable. My own line of research has been somewhat similar, though not undertaken with the same end in view. I have been investigating the gamma rays emitted by the substance usually known as Radium C, a product of Radium emanation, and in doing so I have come across some very interesting magnetical phenomena. Indeed, I have a theory as to the actual nature of the force we call magnetism, but it is not yet time for my discoveries to be given to the world. Mr. Halliday’s experiments and views were exceedingly interesting to me.”
Poirot nodded. Then he asked a question which surprised me.
“Madame, where did you converse on these topics? In here?”
“No, monsieur. In the laboratory.”
“May I see it?”
“Certainly.”
She led the way to the door from which she had entered. It opened on a small passage. We passed through two doors and found ourselves in the big laboratory, with its array of beakers and crucibles and a hundred appliances of which I did not even know the names. There were two occupants, both busy with some experiment. Madame Olivier introduced them.
“Mademoiselle Claude, one of my assistants.” A tall, serious-faced young girl bowed to us. “Monsieur Henri, an old and trusted friend.”
The young man, short and dark, bowed jerkily.
Poirot looked round him. There were two other doors besides the one by which we had entered. One, madame explained, led into the garden, the other into a smaller chamber also devoted to research. Poirot took all this in, then declared himself ready to return to the salon.
“Madame, were you alone with M. Halliday during your interview?”
“Yes, monsieur. My two assistants were in the smaller room next door.”
“Could your conversation be overheard—by them or anyone else?”
Madame reflected, then shook her head.
“I do not think so. I am almost sure it could not. The doors were all shut.”
“Could anyone have been concealed in the room?”
“There is the big cupboard in the corner—but the idea is absurd.”
“Pas tout à fait, madame. One thing more: did M. Halliday make any mention of his plans for the evening?”
“He said nothing whatever, monsieur.”
“I thank you, madame, and I apologize for disturbing you. Pray do not trouble—we can find our way out.”
We stepped out into the hall. A lady was just entering the front door as we did so. She ran quickly up the stairs, and I was left with an impression of the heavy mourning that denotes a French widow.
“A most unusual type of woman, that,” remarked Poirot, as we walked away.
“Madame Olivier? Yes, she—”
“Mais non, not Madame Olivier. Cela va sans dire! There are not many geniuses of her stamp in the world. No, I referred to the other
