Two staff members, Jimmy and Sammy, are aspiring songwriters who make their living writing radio jingles.

When Mary's demonstration record is released to the public accidentally, Taylor's manager threatens to sue O'Hara.

O'Hara goes around town buying back copies of Mary's record and smashing them in the stores, which lands him in jail.

Confusing matters further is O'Hara's new secretary, Polly Kane, who makes her own recording and is thus mistaken for mystery vocalist Mary.

Hot Rhythm was Monogram's biggest production of 1944, with an unusually long running time of 79 minutes, and with the studio's top cameraman Ira H. Morgan and director William Beaudine joining forces to make the economically staged scenes look more elaborate.