So there's this girl who steals $40,000. Her name's Marion Crane (Leigh). She's a secretary at a real-estate office who's hungering to move in with her hunky but destitute long-distance lover (John Gavin). Hence the impulsive decision to palm the cash when a cocky client waves it in her face between double entendres.
Men surround Marion---a cop in shades ogles her with contemptuous suspicion; a used-car dealer prods her with intimidating sales-speak. Even Norman Bates (Perkins), the seemingly mild-mannered clerk she has dinner with at a roadside motel, gets antsy in her presence. But he eventually illuminates her crisis of conscience: "We all go a little mad sometimes," the young man observes, inspiring Marion to renounce her kleptomania and take a cleansing shower. Then Mother shows up.
What was that about madness? Alfred Hitchcock, the jovial purveyor of this influential, still-masterful shocker, implies that we don't know jack about it. A nosy private eye (Martin Balsam) and Marion's overly stubborn sister (Miles) wander around as if on preordained paths, seeking shouting-headline explanations (money! multiple personalities!) to ultimately inexplicable occurrences. The best that can be said is there are bats in the belfry and a well-preserved corpse in the basement. What else can one do but scream?