Based on

Movies like Streamlined Swing (1938)

A group of African-American waiters on a railway believe they have made a deal to secure a railroad dining car that they set up on Wilshire Blvd. in Los Angeles as a diner. To bring in customers, they sing, their voices providing most of the musical accompaniment as well. At the diner, in front of a crowd of swells, the police deliver the bad news.