Christopher Lee is an anthropologist who's discovered a frozen humanoid in Manchuria. He's going to take it back to London via the Trans-Siberian Express. Peter Cushing is Lee's rival, and he's also aboard. Before the train even leaves the station, a man is killed. Once the train starts moving, more and more people die. The setting is of interest here because after the first few minutes, everything happens on the train.
There are a number of twists involving the now-unfrozen humanoid, so I won't reveal them. Let's just say he's hard to kill. Eventually Telly Savalas shows up as the leader of a band of Cossacks. He thinks there are rebels on the train and that they're responsible for the deaths. Savalas starts out over the top and then builds from there. He's obviously having a great time, and his performance is a nice contrast to that of Cushing, who does a fine low-key job. And then there's the mad monk, played by Ángel del Pozo, who gives Savalas a run for his money.
Horror Express isn't a great movie, but it's a good bit of goofy fun. Worth a look if you like this kind of thing. And it's a must for train buffs.