Lights, camera, action!
After breaking his leg running out on a racetrack to get an action shot, photographer L.B. "Jeff" Jefferies (James Stewart) has been stuck in a wheelchair in his Greenwich Village apartment. He's in a full leg cast that's definitely cramping his style. The only thing Jeff finds worse than being trapped in his wheelchair is being trapped by his beautiful model/fashion-editor girlfriend's attention. She (Grace Kelly) is gorgeous, smart, nurturing, financially independent, and she can't keep her hands off of him. See the problem?
It's a hot summer, and the neighbors in the courtyard behind his place open up their windows. For a guy on intimate terms with a long-range lens and a penchant for putting his nose into interesting situations, this is like throwing chuck steak in front of a wolf.
So, he starts watching his neighbors, from the sexy Miss Torso to the crotchety couple who sleeps every night on the fire escape to cool off. There's Miss Lonelyhearts, who entertains imaginary gentlemen, and salesman Lars Thorwald (Raymond Burr), who is married to an irritable woman who spends most of her time sick in bed.
One night, Jeff hears a woman screaming, and he notices Thorwald taking repeated trips out in the middle of the night, carrying his sample case in and out of the apartment. 'Round these parts, we call that suspicious. Could Thorwald have murdered the missus? Jeff starts spying on the guy, getting more obsessive by the moment and roping both his visiting nurse, Stella, and his girlfriend, Lisa, into his schemes.
Jeff calls Det. Lt. Doyle, his policeman buddy, and asks him to investigate. Doyle isn't impressed by the "evidence" and doesn't approve of Jeff's amateur sleuthing. But details keep piling up that prove impossible for Jeff to ignore. A neighborhood dog is found strangled after digging in a flowerbed and only Thorwald doesn't seem surprised by it. Jeff and Lisa send Thorwald a note accusing him of murder so they can watch his reaction when he reads it.
The trick works so well that Jeff ups the ante by calling Thorwald and telling him that he'll go to the police if he doesn't meet him in a nearby bar. The minute Thorwald leaves, Lisa heads over to his apartment and starts looking for evidence. She finds his wife's wedding ring but is interrupted by Thorwald's return. We're gearing up for Gruesome Murder 2.0 when the police arrive, summoned by Jeff in the nick of time. Lisa gets to take a free trip downtown for breaking and entering, but before she goes, she waggles her finger at Jeff to let him know she has the ring.
Turns out, that's not such a hot idea. Thorwald spots it and soon confirms what Jeff has been up to. He pays a social visit shortly thereafter, by which we mean not a social visit at all. Jeff is stuck in his wheelchair, and while he manages to fend off Thorwald for a bit with the clever use of blinding camera flashbulbs, it looks like he's getting a free trip out of that window that he's spent so much time looking through.
The police arrive again in the nick of time, but not soon enough to prevent our hero from taking a tumble into the courtyard below. He survives thanks to a couple of friendly cops who serve as impromptu mattresses, and the police take Thorwald into custody. Jeff, now with both legs in casts, naps happily in his wheelchair while Lisa smiles—having proved to Jeff she's more than just a pretty face.