Schoolmistress on the loose) is a 1941 Swedish romantic comedy film directed by Börje Larsson, who also wrote the script.
Karin Berggren is a strict teacher at Sunninge flickpension, a distinguished boarding school for girls in a venerable old castle in Scania in the south of Sweden.
The night before the inspection Karin and her colleague Bror sneak away to visit a nightclub in Copenhagen.
So by daytime she is a teacher in French and by night a seductive nightclub singer in Copenhagen, under the name Lucy Phillips.
So the colleagues follow her, to see her performance with their own eyes, and there Karin makes her entrance on stage, singing Love's ABC...[1]