To be honest, I'm not sure if there would be much interest in a mystery-themed RP based on a cult TV show that's well over 20 years old ... I guess that's why they call this an "interest check"!
Anyway, I'm thinking of running a group RP loosely based on the events of the show "Twin Peaks". Twenty-two years after the murder of Laura Palmer and the disappearance of FBI Special Agent Dale Cooper, two young girls are found dead under mysterious circumstances in Twin Peaks, Washington. With the words "FIRE WALK WITH ME" carved into the arm of one of the girls, it looks like a long-ago killer may be back on the prowl.
This would be a freeform mystery RP, with supernatural elements. I'm really looking for players who are familiar with the original Twin Peaks series, and who have at least seen some episodes of the show. If I get some interest in this, I'll put up a more fleshed-out outline for this group game and begin asking for character concepts.