“In fact-Dr. Sheppard!”

“About Miss Debenham," he said rather awkwardly. "You can take it from me that she's all right. She's a pukka sahib."What," asked Dr. Constantine with interest, "does a pukka sahib mean?""It means," said Poirot, "that Miss Debenham's father and brothers were at the same kind of school as Colonel Arbuthnot was.""Oh!" said Dr. Constantine, disappointed. "Then it has nothing to do with the crime at all.""Exactly," said Poirot.”

“They conceive a certain theory, and everything has to fit into that theory. If one little fact will not fit it, they throw it aside. But it is always the facts that will not fit in that are significant.”

“Proof must be solid break walls of facts.”

“If the fact will not fit the theory - let the theory go”

“One of us in this very room is in fact the murderer.”

“When the fact doesn't meet the theory then let go the theory.”