 Composer-pianist Hoagy Carmichael, playing the sidekick role, added realism to the film and gave Douglas insight into the role, being a friend of the real Beiderbecke.Doris Day starred as Jo, a young woman who was infatuated with the struggling jazz musician.This was strikingly opposite of the real-life account in Doris Day's autobiography, which described Douglas as "civil but self-centered" and the film as "utterly joyless".