The case in question is episode 50 of My Little Pony: Friendship Is Magic – “MMMystery on the Friendship Express“
Murder on the Orient Express is one of Agatha Christie’s most famous mysteries with countless remakes and homages over the years. But one of the most unexpected places to see such a tribute is My Little Pony: Friendship Is Magic. While Twilight Sparkle is not investigating the brutal stabbing of criminal Pegasus who previously was caught up in a tragic kidnapping, the story is fairly faithful to original. Over all it is a clever little episode that manages to take a classic mystery and make it accessible to a younger audience. It even manages to reference several other famous mysteries and spy stories in the process.
Lum is the type of show where you never know what the next episode will be about, it is a rather odd and varied assortment of short comedies running the gamut of success. But you always expect comedy, and maybe the occasional tender moment, so this episode comes off as particularly creepy. And even the few attempts at silly just cement how bizarre the tale is. 
