I always give early-1930s movies the benefit of the doubt, and I'm doing so here. An actor working alone in a radio studio room is murdered while reading his lines (in which his character is murdered). Someone in the studio building at the time killed him, but whom? There are only a few possible culprits, and most aren't very well defined characters. A few years later, this probably could have been a very good movie, but it's barely passable here. I suspect much of the appeal of this film when it was released came from the behind-the-scenes look at a working radio studio, with actors in multiple rooms, and orchestra in another, and crew in still others. You even get a song and a dance number, although the appeal of a dance number on radio, including dancers in full costume, escapes me.
If you enjoy 1930s crime/mysteries, then this is worth a watch. The detective doesn't define himself particularly well, but the genre plays out reasonably true to form. I gave it a 6 for slightly better than average.