A good idea for a mystery story could be centered around a series of anonymous letters that are being sent to different people in a community. These letters contain cryptic messages that seem to be leading to some sort of impending doom. The detective or the main character has to decipher the codes in the letters and figure out who is sending them and why. Also, a mystery about a locked room where a person is found dead with no obvious way in or out is always interesting. Or perhaps a story where a young heir suddenly disappears on the night before they are set to inherit a large fortune.
You could base a mystery story on a cursed painting. The painting has a strange history. People who own it start experiencing bad luck or seeing strange apparitions. Is it a hoax, or is there something truly supernatural about it? Also, having a detective character who has his own personal demons can add depth to the story. He's trying to solve the mystery while also dealing with his own problems, like a drinking habit or a broken relationship.
A murder mystery set in a small, idyllic village. A wealthy landowner is found dead. The local villagers all seem to have motives. The baker might be angry because the landowner wanted to raise the rent of his shop. The gardener could be suspect as he was often mistreated by the landowner. And there could be a mysterious stranger who was seen in the village around the time of the murder. The key to solving the mystery could be a rare flower found at the crime scene which is only grown in the gardener's greenhouse.
A good idea for a short mystery story is a cursed object. For example, a beautiful antique mirror that brings bad luck to anyone who looks into it. People start having accidents or misfortunes after looking at it. The mystery could be about finding out the origin of the curse and how to break it. Another is a missing heirloom that has a lot of sentimental value. It was last seen in a particular room of an old mansion. The main character has to search through old family secrets and hidden passages to find it. Also, a mystery about a strange symbol that keeps appearing around town. No one knows what it means, and it seems to be linked to some sort of underground cult or a long - lost treasure.
A horror mystery story could revolve around a haunted mansion. A family moves in, not believing the rumors of it being haunted. Strange things start to happen - objects move on their own, they hear unexplained whispers. As they dig deeper, they find out that the previous owner was a deranged serial killer who hid his victims' bodies in the walls of the house, and their spirits are now trapped and angry.
A small town is haunted by a series of disappearances. Every full moon, someone vanishes without a trace. The main character, a detective, starts to investigate. He notices that all the victims had visited an old, dilapidated mansion on the outskirts of town before they disappeared. When he goes to the mansion, he finds it filled with strange symbols and a locked room. As he tries to break into the room, he hears a deep growling noise. The mystery could revolve around a cult that used to operate in the mansion and is now kidnapping people for a dark ritual.
One idea could be a murder in a small, seemingly idyllic town. The victim is a well - liked local figure. The detective discovers that there are many secrets hidden among the townsfolk. Everyone seems to have a motive, from the local business owner who was in financial trouble with the victim to the jealous neighbor. Clues start to emerge, like a strange symbol found at the crime scene that leads the detective on a wild goose chase through the town's history.
You could use 'The Shadow in the Alley'. It gives a spooky and mysterious feeling. Just the thought of a shadow in an alley makes the reader wonder what's lurking there. Is it a person? A supernatural being? It sets the mood for a mystery.
One idea could be a missing heirloom. The story could start with an old family's most prized possession disappearing overnight. The main character, a young detective, could be hired to solve the mystery. He or she then discovers strange footprints around the scene and some cryptic notes left behind.
Read a lot of mystery novels and watch mystery movies. This exposes you to different plot devices and mystery - solving techniques. For example, you can learn how to create red herrings from the works of Agatha Christie. Another way is to think about real - life mysteries like unsolved crimes or historical enigmas and adapt them into your story. You can also start with a simple question, like 'What if a person woke up in a place they didn't recognize with no memory of how they got there?' and build a mystery around it.