Sounds like mystery episode taking place on...a train?
Well, time to hand this one off to a tourist railroad--the Fillmore and Western, to be exact. Having perfected the "Mystery Dinner Train", having close ties to Hollywood, and a scenic rail line with a ready-to-run steam locomotive (F&W #14), they could easily bring ponies to the real-world rails.
Here's a shot of FWWR #14 in action, hauling a charter train:
All they really need is some modified station signage to ponify the line (Piru = Ponyville, Fillmore = Fillydelphia, the list could go on!), some ponified pullmans, and plenty of costumes...and they'd be in business!
Hey, if they're looking for a car attendant...sign me up!
