A man is shot In the hotel of an imaginary South American country. Clarence and Montès, two inspector students, must solve this murder, but they don't know that dead guy is the USA public enemy No.1.

Gilbert, poet and singer, is about to marry Lilette but deep inside himself he is not quite sure that she is the woman he needs. That is the reason why he has made up an imaginary woman, Frédérica" to whom he writes love letters, actual ones this time. When Lilette finds one of these, she sees red. Théodule, one of Gilbert's many friends, sets out the problem with the help of Claudine, his own girlfriend, posing as Frédérica. After Gilbert and "Frédérica" have played a phony breakup scene in front of Lilette, things seem to come right when... another Frédérica appears...