Much like Psycho, nothing is what it seems and characters that appear to be permanent are not.
A fan of bait-and-switch storytelling that starts off as one thing and then suddenly twists around, catching the viewer off-guard and feeling unsafe, De Palma used the framework of 1960's " Psycho " for his own splendidly bizarre narrative.
This one uses Alfred Hitchcock's Psycho as a starting point before veering off in its own deliciously twisted direction, centering on a sexually frustrated housewife (Angie Dickinson), her patient therapist (Michael Caine), an imperiled prostitute (a wonderful Nancy Allen) and a razor-wielding psychopath.
This time, he's channeling mostly "Psycho" but also "Vertigo" and his own "Carrie".
It's one of the most overt of De Palma's "look at me, I'm a cinephile" homages to Alfred Hitchcock, and especially to Psycho , a film from which it openly borrows enormous chunks of its plot and narrative structure.
And later, a bloody attack with a straight razor can’t help but steal camera angles and choreography from “Psycho” (along with the overt thefts of the ideas to remove a main character when least expected, the sequence in the shower, a transvestic nutter, and a lengthy exposition at the conclusion to spell everything out for the unobservant audience).