We hurried back to London, and the following day saw

us en route for the Continent. With rather a rueful

smile, Poirot observed:—

"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 Surete, 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, dif 40

50 Agatha Christie

ficulties 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 any one 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 co-worker 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

THE BIG FOUR 51

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