Castle is home, mostly alone, in a wheelchair after a skiing accident, bored out of his wits just before his birthday. After a while, he actually picks up a pair of binoculars Alexis gave him to play Rear Window. Indeed, right across the street a foxy resident betrays her studly husband with a younger hottie. Shortly after, the cheated husband finds his rival's hat, wields a knife and seems to dispose of the corpse while she isn't seen again. Yet his NYPD team mates only reluctantly investigate and can't find any proof. Castle becomes obsessed with the possibility that he witnessed a murder, while Beckett grows increasingly upset with his mania and sets out to find out the truth one way or the other. That's when things take a surprising and shocking turn...
- Castle returns home with an injured leg, acquired while trying to show off during a ski trip with Beckett. Immobilized and homebound, he starts to take an interest in the activities of his neighbors. As an homage to Alfred Hitchcock's film Rear Window, Castle, while looking out his window, thinks that he has witnessed a murder and enlists the help of Alexis and Kate to help him uncover the truth.