You may be looking for the Hardcastle & McCormick zine Casefiles.
|Trope · Genre|
|Synonyms:||case file, case fic, detective story|
|Related:||Action-Adventure, Relationship Story, Get'em, Lay Story|
|See Also:||Virtual Season|
|Tropes · Slash Tropes · Tropes by Fandom|
|Click here for related articles on Fanlore.|
In many television shows, particularly police procedurals, buddy cop shows, and some medical dramas such as House M.D., each episode revolves around the main characters being presented with a particular mystery or case, which they then investigate and bring to a conclusion. Case fic is a type of fanfiction that mirrors the format of the source text, featuring an 'A' plot that focuses on a case similar to the cases featured on the show, and usually a 'B' plot that deals with the characters' personal issues or interactions.
In general, case stories are similar in structure to the show they are based on. However, they may be radically different in tone, and often bring in elements or subplots that wouldn't be present in the show, such as explicit sex, slash, or, occasionally, supernatural occurrences. Case fic is often described as being "just like an episode of the show," or alternately, "just like an episode of the show, except with sex."
In X-Files fandom, the term "case file" is used instead of "case story."
Terms like 'casefic' are often used to distinguish plottier stories from PWP or WAFF-y curtainfic. Examples of tropes that often occur in case stories (whether or not they would be likely in canon) include:
- Pretend Couples and characters going Undercover in a Gay Bar
- "murder" cases involving Presumed Dead characters
- characters going undercover as prostitutes
- supernatural crimes, often ones that involve vampires
...casefic -- plot-focused, about an investigation, with a setup similar to an episode. Casefic is a weird animal. Lots of fans like it in theory, but it's very difficult to do well. But I don't think many fans want their casefic to feel exactly like just another episode of the show. I'm one of those fans who tends to enjoy fic that gives me more of the things I see in the canon show, but the keyword here is more. Most casefics need something more than what a canon episode can provide. A fic that is "like an episode" usually isn't satisfying if it reads like an episode script tweaked into narrative rather than script format. It needs some kind of extra element, usually an It's Personal for the main characters, or worldbuilding, or added background or context for the canon events: say, it's like an episode, but it's like a special episode centered on a crisis with a main character... Or it has a meaningful or illuminating personal subplot (not necessarily a serious one, mind you). Or it's like an episode event-wise, but with an added layer of personality when it comes to how the main characters observe it or talk about it or are affected by it. Fanfic, even casefic, has different strengths and priorities than episodes. 
- Torch's X-Files stories Ghosts and Lovers were case-driven stories that explored mysteries much like those dealt with on the show, with the addition of homoerotic themes and explicit m/m sex.
- List of stories on AO3 that use the casefic tag