The Mystery of the Twelfth Floor

After moving to a scenic resort city, the heroine and her family are invited by their warmhearted neighbor to join a "big family" made up entirely of people from out of town. The members aren't related by blood, but they're closer than family, and their harmonious relationships make the heroine's family feel the warmth of home.

But their good times don't last. Some time later, the heroine learns that the place where they often gather is actually a haunted house. Two years ago, a bizarre murder took place there. Her neighbor had been organizing get-togethers at her home because she was afraid to be alone.

The revelation casts a shadow over the heroine, but she never expects that even more terrifying events are just around the corner. After they move there, members of the big family are murdered one after another. The police determine that the killer is someone they know. The heroine can't understand why this is happening. Who is the killer, and what is their motive? As the investigation unfolds, an unexpected truth gradually comes to light...