Ink ribbon red

 
A group of friends gather in a country house for a birthday party. At their host's request, they each write a short mystery. They draw names from a hat: in each story, one of the group is the killer, and another the victim. Of course, when given such a task, it's only natural to use what you know. Secrets. Grudges. Illicit love. It's just that once you put it in a story, the secret is out. Oh, and just one more thing: this is a story that ends with a murder.