First, Poirot interrogates MacQueen, Ratchett's employee. Here's what we learn:
When MacQueen first finds out about Ratchett's death, he assumes it was murder.
MacQueen was Ratchett's secretary for a little over a year. They met in Persia, where MacQueen had come to get into the oil business.
MacQueen busted in that business. He met Ratchett in a hotel, and Ratchett offered him a job. They've traveled around together ever since.
Ratchett's full name is Samuel Edward Ratchett, and he's American. He never spoke much to MacQueen about his life. He had no relations to speak of.
MacQueen's theory: Ratchett was running from someone or something, and left his identity behind in America.
A few weeks ago, Ratchett began getting threatening poison pen letters.
MacQueen shows Poirot the letters. They are gangster-like threats.
Poirot notes their "monotonous" style and that they were probably written by two people, each writing different letters of the alphabet (1.6.87).
Poirot tells MacQueen that Ratchett asked for his help; MacQueen is surprised.
MacQueen admits that he didn't really like or trust his employer, though they were on good terms.
The last time MacQueen saw Ratchett was around 10 p.m., about some pottery in Persia.
The Ratchett received the most recent threatening letter on the morning the train left Constantinople.
MacQueen's full name is Hector Willard MacQueen and his address is in New York.
MacQueen leaves and M. Bouc and Poirot discuss his interview. He seems honest enough. M. Bouc proposes that he is innocent, but Poirot says he suspects everyone "till the last minute" (1.6.127).
Poirot admits, though, that frenzied stabbing is not in line with MacQueen's character. M. Bouc says, no, it is more in line with someone of "Latin temperament" or a woman (1.6.128). (Warning: stereotypes ahead.)