Based on the slim novel by a mostly forgotten Robert Bloch, the film opens with Marion Crane, played by Janet Leigh, stealing a tidy sum of money in an attempt to realise her relationship with her partner, the recently divorced Sam. Her theft, more a crime of a passion than anything premeditated, is the focus of the first part of the film, and Leigh does a decent job of holding the film together until she arrives at the now culturally famous Bates Motel, a quiet, forgotten thing on the wrong part of the highway. There, she meets Norman, a man who is controlled by his mother, an angry, shrill woman seen in shadows on the top floor of their house. Played by Anthony Perkins in a roll that he would attempt to resurrect another two times, Norman is a strange, off-kilter man, who over the course of the film will be revealed to be a little more, much to the sorrow of Marion, and a handful of others.
As I said, the strangest thing about the film is the nature of it, and how easily it could have been much, much worse. It's perhaps no surprise that Perkins' attempt at two sequels look and sound awful, while the shot for shot remake by Gus Van Sant is uniformly disliked and considered poor against the original. Van Sant isn't a terrible director, and can be, at times, quite good--but he doesn't have the ability that Hitchcock had to elevate his film above it's subject material, which in the hands of another, would be terrible, b-grade trash.
Yet, that's not the true mark of Hitchcock's success with the film. No, the success of Psycho comes through the the melding of what is essentially four set pieces into a uniform whole, ending with the most difficult of the four, which is that of the psychiatrist explaining the mental illness of Norman Bates. Taken by themselves, the story of the unsatisfied woman, Marion Crane, the detective who has been hired to find her, the suspicious sister, and the psychiatrist, all form different, distinct quarters of the film--though to call them quarters is a lie, since they are not perfectly divided for time--and it is to Hitchcock's credit that he can use the Bates motel and Norman himself to bring all four narratives together, and make it appear as seamless as he does.
It is a pleasure to watch, even fifty years later.