Touch of Evil (1958).
I think this is Orson Welles' most acclaimed film after Citizen Kane. Watching it right after The Stranger from 1946, it's incredible how much Welles has changed. I don't know if any (prosthetic) makeup was used to make him look this way or whether it was all purely how he looked for real, but the change is enormous. He has clearly put on a lot of weight, but his face looks very different too.
The film starts off with the famous scene of a time bomb being put in a car passing the U.S./Mexican border. The car is followed driving through town and across the border in one long take, with the woman in the car saying she hears a ticking noise in her head. After the explosion of the car, drug enforcement official Miguel Vargas (Charlton Heston) who's in town with his wife Susie (Janet Leigh) takes an interest in the case, and the film is essentially about him dealing with the corrupt (and corpulent) police captain Hank Quinlan (Welles), planting false evidence and implicating Susie, and his close partner Pete Menzies.
The film also has roles for Zsa Zsa Gabor (more of a cameo), Marlene Dietrich and Dennis Weaver as the (rather comical) manager of a motel. The story is relatively simple, but it's more about the characters and the mood. The final scene is strikingly filmed against the backdrop of an oil field, with the drilling rigs and pumpjacks throwing ominous shadows over the characters.
It also has Janet Leigh two years before Psycho caught up in another motel where bad things are happening to her.