Of course, The Thin Man isn't really a Thanksgiving movie, but it is for a good stretch a Christmas movie. (Thanksgiving and Christmas get conflated in all sorts of ways, about which I will probably post more at the end of the week.) And it is also a murder mystery, with the movie dividing itself almost perfectly in two: in the prologue a young couple announces their intention to be married "right after Christmas", soon we meet Nick Charles and his wife Nora as she returns from a shopping excursion and spills wrapped Christmas presents across a nightclub floor, then we attend a Christmas party thrown by the Charleses, followed by a Christmas Eve altercation between Nick and a lowlife named Morelli, and the subsequent police investigation intruding on Nick and Nora's idle Christmas morning. As Nick, the former detective, is fully drawn into the case of the killing of Julia Wolf, the movie pivots away from the yuletide trappings, and becomes more focused on the police, the suspects, and ultimately the solution to the mystery.
I enjoy a good mystery now and then but I'm not fanatical about the genre. I'm interested in how mysteries are constructed, and in general I find puzzles and riddles entertaining, which usually becomes the major draw for me when I'm reading or watching a mystery. I try to figure out the solution along with the protagonist, which is no doubt a holdover from the many Encyclopedia Brown books I devoured as a kid. But not all mysteries provide enough information to the audience for them to solve the crime; some have the protagonist crack the case and explain it to the audience in the end, and sometimes the mystery solves itself via a convenient confession or some other lucky break for the gumshoe.
Spoiler warning, I suppose, by way of a slight Wikipedia digression. You may look up either the movie version of The Thin Man or the entry for the Dashiel Hammett novel on which it's based, and Wikipedia will not spoil the solution to the central mystery. This is a story that came out about 80 years ago. It is older than the Wizard of Oz (It was all a dream!). I will be far less circumspect than Wikipedia, in part because of the old news nature of the information, but just as much because I don't think the solution to the mystery is either (a) terribly ingenious or (b) the point of the movie. But, be that as it may, proceed forewarned.
The lawyer did it. Nick gathers all of the suspects and other interested parties, including the police lieutenant handling the case, for a formal dinner party, and extemporizes about the crimes and how the prime suspect thus far was actually the first one killed and has been framed in absentia for all the others. All Nick is doing is speculating wildly about how the murders are connected and what the motives must be, until finally his relentless questioning of someone he believes is not the killer (but also whom he believes knows the killer's identity) causes the real killer, the first victim's lawyer, to panic and reveal himself in an ill-fated attempt to shoot his way out of the dinner party. In an upper-floor hotel room. Filled with police officers. Nick states repeatedly that the plot to kill Clyde Wynant, steal his fortune little by little while keeping up the ruse that Wynant was alive, and subsequently eliminate potential witnesses and position Wynant as the murderer, was very clever, but the lawyer's final, doomed escape plan does not paint him as a true criminal genius.
I know, at the least, that the resourceful detective tricking the guilty party into giving himself away is a venerable old trope of the mystery genre, and I will give The Thin Man credit for the fact that at one point Nora asks Nick how he can know all the things he is asserting, and he admits out the corner of his mouth that he doesn't really know any of it for certain, but it's the only version of events that makes sense. Really, it's the interplay between Nick and Nora that not only unifies both halves of the film, holiday merry-making on one side and mounting dead bodies and double-crosses on the other, but also makes The Thin Man so memorable and so beloved by many. If a mystery fan were to encounter The Thin Man looking for a classic whodunnit, I imagine they'd be somewhat underwhelmed. But if a fan of classic Golden Age Hollywood banter came looking for a hangout movie, one that makes the viewer wish they could step into the screen and enjoy cocktails and conversation with the main characters, The Thin Man would hit the mark. Its secret weapon is the easy charm of both William Powell as Nick and Myrna Loy as Nora, and the way the two of them combine as something greater than the sum of their parts. Together they walk a fine line, engaged in a constant running battle of sharp-tongued wits something like a fencing match. Mr. and Mrs. Charles are clearly in love, not in a sickeningly sappy way but also not in an aggressively antagonistic way. It's simply a delight to be allowed into their world for a little while.
Plus, the film ends with Nick leaning suggestively into Nora's berth on a sleeper train, a pan up to their dog Asta covering his eyes with a paw, and then a cutaway to an exterior shot of the train racing away in the night to the strains of "California Here We Come", and that is just about the most magnificent Hays Code euphemism pile-up I can possibly imagine.