I had a DnD character who owned a private eye firm with is brother. He and his brother were investigating this drug running gang that also happened to be a cult of Nyarloathotep. The leader of which would kidnap people, mutilate their genitals and then use some kind of dark ritual to merge two of these unlucky victims bodies into a hulking grotesque monstrosity.
His brother had recently gone missing and so he was investigating their suspected hideout for information. Eventually he is able to find out that his brother was killed by the group and the leader of the gang had left the area.
After that he started keeping a diary of events, however he wrote them in the form of letters to his dead brother.
If you think you can use any of that please feel free.