"We are much obliged to you, M. Zeropoulos," said Fournier politely.

"This blowpipe and dart - you think you would be able to identify them?

At the moment they are in London, you understand, but an opportunity will be given you of identifying them."

"The blowpipe was about so long -" M. Zeropoulos measured a space on his desk. "And so thick - you see, like this pen of mine. It was of a light color. There were four darts. They were long pointed thorns, slightly discolored at the tips, with a little fluff of red silk on them."

"Red silk?" asked Poirot keenly.

"Yes, monsieur. A cerise red, somewhat faded."

"That is curious," said Fournier. "You are sure that there was not one of them with a black-and-yellow fluff of silk?"

"Black and yellow? No, monsieur."

The dealer shook his head.

Fournier glanced at Poirot. There was a curious satisfied smile on the little man's face.

Fournier wondered why. Was it because Zeropoulos was lying? Or was it for some other reason?

Fournier said doubtfully: "It is very possible that this blowpipe and dart have nothing whatever to do with the case. It is just one chance in fifty, perhaps. Nevertheless, I should like as full a description as possible of this American."

Zeropoulos spread out a pair of Oriental hands.

"He was just an American. His voice was in his nose. He could not speak French. He was chewing the gum. He had tortoise-shell glasses. He was tall and, I think, not very old."

"Fair or dark?"

"I could hardly say. He had his hat on."

"Would you know him again if you saw him?"

Zeropoulos seemed doubtful.

"I could not say. So many Americans come and go. He was not remarkable in any way."

Fournier showed him the collection of snapshots, but without avail. None of them, Zeropoulos thought, was the man.

"Probably a wild-goose chase," said Fournier as they left the shop.

"It is possible, yes," agreed Poirot. "But I do not think so. The price tickets were of the same shape and there are one or two points of interest about the story and about M. Zeropoulos' remarks. And now, my friend, having been upon one wild-goose chase, indulge me and come upon another."

"Where to?"

"To the Boulevard des Capucines."

"Let me see. That is -"

"The office of Universal Air Lines."

"Of course. But we have already made perfunctory inquiries there. They could tell us nothing of interest."

Poirot tapped him kindly on the shoulder.

"Ah, but, you see, an answer depends on the questions. You did not know what questions to ask."

"And you do?"

"Well, I have a certain little idea."

He would say no more and in due course they arrived at the Boulevard des Capucines.

The office of Universal Air Lines was quite small. A smart-looking dark man was behind a highly polished wooden counter and a boy of about fifteen was sitting at a typewriter.

Fournier produced his credentials and the man, whose name was Jules Perrot, declared himself to be entirely at their service.