I’m going to purpose something: There are two ways a writer can write a mystery.
The first is in the manner of a curtain being slowly pulled back on an event. The investigator and the reader learn information at the same rate. The problem with this method, and perhaps with police work in general, is that often you don’t have (and may never have) all the information.
The second is in the manner of a jigsaw puzzle. All the pieces are placed out in the open and the detective and the audience piece them together. The problem with this method is that it make it easy for the writer to cheat—to hold a piece back (the ingenious reveal of information that only the detective has gleaned), or to add a piece from a different puzzle (the red herring).
I’m not a fan of the second.* That said, I was pretty sure that was the method Christie uses. Murder on the Orient Express is the first Christie novel I’ve read, and it is the one I knew the ending to. While she uses some of those cheats, there’s sort a fourth-wall-meta aspect to this story that I wasn’t expecting. The characters themselves comment on how much like a police novel the events are. Some clues are tagged as so obvious that they are disregarded because they were planted to look like clues. That kind of a wink to the process endeared me.
One thing that Christie does very well is differentiate her characters. For a fairly short book, it has a big cast. She establishes key detail for each and does a masterful job giving them personality through dialog. Much of this book was the characters being interviewed by other characters, by stories being told and retold, and Christie avoids it becoming tedious by giving each telling its own separate voice.
*Okay, Doyle does it too in his Sherlock Holmes stories, and I love Doyle. What Doyle does: He puts us in the head of Watson, someone who is pretty much the reader. And then has Holmes insult our intelligence because we can’t keep up. Somehow, this makes us love the character all the more.