Plot
Sam Dalmas is an American writer vacationing in Rome with his English model girlfriend, Julia, while trying to overcome his writer's block. They are preparing to return to the United States in two days.
While walking home one evening, Sam witnesses a woman being attacked in an art gallery by a male figure wearing a black raincoat and black leather gloves. Attempting to intervene, Sam becomes trapped between the gallery's mechanically operated sliding glass doors while the assailant escapes. The woman, Monica Ranieri—the wife of the gallery's owner, Alberto Ranieri—survives the attack and the local police confiscate Sam's passport to prevent him from leaving the country. The assailant is believed to be a serial killer who has so far murdered three young women across the city, and Sam is an important witness.
Sam is haunted by what he saw that night, convinced that some vital clue is evading him, and he resolves to help Inspector Morosini in his investigation. He visits an antique shop where the first victim worked, discovering that the last item she sold on the day of her death was an eerie painting of a man in a raincoat stabbing a young woman amidst a snowy landscape. When the killer phones Sam at his apartment, threatening to kill Julia unless he drops his investigation, he records the call.
Sam visits the artist of the painting in a nearby town, under the pretense that he wants to buy a painting. The artist tells Sam that the painting in question is inspired by an actual attack on a young woman that occurred ten years earlier. Meanwhile, the killer attempts to attack Julia while she is alone in Sam's apartment, but Sam returns just in time to save her, and the killer flees.
The police manage to isolate an odd cricketing noise in the background of the telephone call recording, which is later revealed by Sam's ornithologist friend Carlo to be the call of a rare bird from the South Caucasus known as "the bird with the crystal plumage" due to the translucent glint of its feathers; the only specimen in Italy is kept in a zoo in Rome. Sam, Julia, Carlo and the police immediately go to the zoo, where Sam observes that the Ranieri apartment overlooks the bird's cage. When screams are heard from the apartment, Sam and the others rush over to find Monica and Alberto struggling over a knife. When the police intervene, Alberto falls out the window onto the sidewalk below. As he dies, he confesses to all the murders.
Realizing that Julia has disappeared, Sam eventually tracks her down to a dark apartment, where he finds Carlo dead and Julia bound and gagged. He then turns around to see Monica in a black raincoat, laughing hysterically. Sam soon realizes that what he witnessed that night in the gallery was not Monica being attacked, but Monica attempting to kill Alberto. She flees, and he pursues her to the art gallery. There, Monica drops a heavy, spiked sculpture onto Sam, pinning him to the floor. She begins taunting him with a knife, and as she prepares to kill him, the police—who were notified by an escaping Julia—burst in and apprehend her. Sam is freed, and Monica is taken to a psychiatric hospital.
It is revealed through a television interview with a psychiatrist that Monica was the victim of a traumatic attack ten years before. Seeing the painting of the attack drove her insane, causing her to identify with the assailant and not the victim. Alberto likewise suffered from an induced psychosis, helping her cover up the murders and committing some himself. Sam and Julia are reunited and fly back to the United States.
