Even non-fans of RKO Radio's "Mexican Spitfire" series will garner a few healthy laughs from Mexican Spitfire's Baby. This time around, tempetuous Carmelita (Lupe Velez) and her staid American husband Dennis (Charles "Buddy" Rogers) adopt a French war orphan. Imagine Dennis' surprise and Carmelita's dismay when their adopted "little girl" turns out to be voluptuous blonde Fifi (Marion Martin). As if Carmelita's jealous rages weren't bad enough, Fifi's equally jealous fiance Pierre (Fritz Feld) shows up, demanding satisfaction from Dennis in the form of a duel. As always, it's up to Dennis' Uncle Matt (Leon Errol) to straighten out the mess -- and also as always, Uncle Matt is required to disguise himself as his British lookalike Lord Epping.