Jack Bailey, who plays the quiz show host at the beginning of the film, became famous shortly afterward as host of the highly popular 1950s TV series Queen for a Day (1951).
Although it's never stated as such, the train is apparently the New York Central's "Twentieth Century Limited" as it runs practically non-stop from Chicago to New York--although it isn't quite as luxurious as the real thing. The express-limited stop trains could make the journey in about 16 hours at an average speed of 60 mph (97 km/h). One train in each direction ran daily, departing late afternoon and arriving mid-morning.
Intended as the first of a planned film series with stars Marjorie Main and James Whitmore. This an attempt by MGM to replicate the success of their earlier "Thin Man" series of crime solving films, which had co-starred Myrna Loy and William Powell, and were based characters created by Dashiell Hammett.
The film was based on the short story "Once Upon a Train, or The Loco Motive"; a collaboration between Craig Rice and Stuart Palmer, which was later collected in short-story collection People vs. Withers and Malone (1963). Rice wrote stories featuring lawyer John J. Malone while Palmer was known for the Hildegarde Withers stories. In the short story, these famous fictional detectives meet. However, MGM couldn't get the rights to Palmer's character, and so Withers was completely rewritten to become Mrs. O'Malley.
The "Treasure Island" radio quiz show that calls Marjorie Main at the beginning of this film would later serve to "inspire" the similar pirate-themed TV game show in How to Succeed in Business Without Really Trying (1967).