Stephen McKeon takes over the role of composer from Christopher Gunning in this episode.
Poirot: I shall be your avuncular.
Katherine Grey: Oh, yes, an avuncular, that's exactly what I need.
Poirot: Papa Poirot, he is at your disposal.
Derek Kettering: Excuse me, gentlemen. If I may interrupt proceedings for a moment? La Roche, there was something I was meaning to give you. Ah, yes, here we go.
(punches La Roche)
Derek Kettering: (to Ruth Kettering) I've never thought of you as a cow. Perhaps as a horse - in the betting sense.
Lady Tamplin (meeting Poirot): This is so exciting, I can hardly breathe!
Poirot: There is something about that gentleman which displeases you?
Van Aldin: I see no gentleman. I see Derek damn Kettering, my damn gold-digging son of a bitch son-in-law!
Poirot: Monsieur Van Aldin, may I have a moment?
Van Aldin: No! Damn it, Poirot, I've had it with your moments!
Lady Tamplin: Ah, here they are at last! Katherine, this is my daughter Lenox. And this infant is my husband.
Lenox: He's not my father, obviously.
Corky: Oh, no!
Lenox: That would be the astonishment of science.
Poirot: The greatest jewel thief in living memory, without a doubt. But do not be the mere lunatic.
Mirelle: I was in bed all night. If you seek corroboration, interrogate my pillow.
This episode is based on Agatha Christie's book The Mystery of the Blue Train (1928), which was an expanded version of her short story The Plymouth Express (part of the collection The Underdog and Other Stories, 1926) - so of course the two Poirot episodes based on them have similar plots.
The Mystery of the Blue Train was first broadcast on A & E in the U.S., on December 11th, 2005, before its first U.K. screening on New Year's Day, 2006.
Agatha Christie described The Mystery of the Blue Train as "easily the worst book I ever wrote".
Katherine Grey: I'm going on to Vienna. I'm catching the Orient Express. The idea thrills me, but I suppose you've been on it millions of times.
Poirot: Not once. But I must!
This reminds us of Agatha Christie's famous Poirot book, Murder on the Orient Express, which has not yet been adapted for this series. Perhaps it will be filmed soon?