Seven Blood-Stained Orchids (Italian: Sette orchidee macchiate di rosso) is a 1972 giallo film directed by Umberto Lenzi, who also co-wrote the screenplay.

A killer is driving around the streets of Italy looking for a specific victim. The killer breaks into her home and kills her, before catching a glimpse of the woman's daughter, Ines, in a photograph before leaving. Later, he poses as an escort and kills her in a field. Elsewhere, Giulia Torresi is picking a dress for her marriage to Mario, a wealthy clothing designer, when she receives a mysterious call, who hangs up when asked their identity. That night, another mysterious call is received by a partygoer named Kathy. The caller is revealed to be close to the party. Kathy is later followed home and killed.

A now newlywed Giulia is attacked and presumably killed on a train. However, the funeral was staged in an attempt to catch the killer. Giulia is alive, but is unable to remember the face of her attacker. While the police suspect Mario, Giulia recognizes one of the previous victims as a fellow employee at the hotel she formerly worked at. A suspect is pinpointed by Giulia recalls a lover of said employee, who was outed to the police by Giulia for stealing from the hotel. The suspect, Rau is brutally interrogated by Vismara's fellow detectives. He proclaims his innocence, but fails to give a strong alibi.

Once free from recovery, Giulia second guesses herself and confesses to Mario that she thinks she's accused the wrong man. In the car, she notices that Mario suspiciously has the exact half moon plaque left behind at each murder scene. Giulia subsequently remembers a vague memory of a frequent guest at her hotel who shared a similar half moon on their key chain. She and Mario race over to the hotel where she had worked. They do not find out anything. Whilst driving back however, she remembers that the names of the previous guests must be legally kept in an official hotel register. They find that the page of the particular date she remembers had been suspiciously ripped out. The page is soon discovered and is looked over by Mario and Giulia. As it turns out, the mystery person, whom she remembers to be an American man's name, is missing. What is present is a list of women: Anita Ferri, Kathy Adams, Elena Marchi, Concetta de Rosa, Anna Sartori, as well as Ines and Giulia who had worked at the hotel.

After not being able to relax and have a proper honeymoon, Mario and Giulia return to Italy to carry out their own investigation, starting with paying the third woman on the list a visit. Said woman, Elena Marchi now resides at a home for the mentally unstable. Once they finally come across the home, Mario goes into the building while Giulia stays in the car. However, they are too late, as Elena is dead. Mario chases the figure into a dark corridor where he is slashed on his shoulder. After this, Giulia catches a lengthy glimpse of the killer as he is escaping. However, she is still unable to describe the murderer to the authorities. Suspicions are cast on Mario.

The following day, Vismara pays Concetta De Rosa a visit. He informs her that she might be in danger of being next. Mario, now strictly focused on finding the identity of the American man, goes to a sketch artist. A sketch is developed of the man, prompting Mario to go and see if anyone recognizes the sketch. These areas include a parish house where a friendly farsighted priest is introduced to the illustration. He draws a complete blank and sends Mario to a local hangout for artists. One student recognizes the man as a friend of someone named Barrett. Mario finds Barrett, who recognizes the sketch as someone named Frank Saunders. From what he understood, Frank got “hung up” on some girl and never saw him since. Mario realizes that one of the women on the list might be the girl. An odd circumstance comes up when the parish priest, briefly seen during Mario's investigation, informs the police that the teacher, Concetta de Rosa, had not attended church as usual. The police soon find her dead in a confession booth. The killer is subsequently dubbed "The Half Moon Maniac".

Mario receives a clue to where Frank Saunders might be located from an anonymous tipster. After going to the address stated, Mario finds out that his suspect, Frank Saunders, had died in an automobile accident two years prior. Anna Sartori, a name not explored much on the list, arrives in Italy only to be immediately confronted by the police. Her arrival is also being watched by The Half Moon Maniac. Anna's husband explains she experienced a traumatic event of sorts while briefly living in Italy. Meanwhile, Mario finds himself at the hospital where Frank had died. He meets with a professor who believes Frank's death was caused by someone else behind the wheel. The professor thinks that it is the woman he got hooked on.

With all this new information, Mario bursts into Barrett's home, believing he is somehow involved in the killings. He however finds Barrett drugged. He returns to the parish house to see if the priest knows the name of the minister who officiated Frank's funeral. Mario is hopeful that the minister will remember some of the people who had been in attendance at the funeral. The priest gets this information for him, but to no avail.