Voir sur FrenchStream. Great excitement in the Principality of Allegretto. Professor Sound, owner of a sanatorium for musical instruments, has come up with a sensational invention: the music pill. Once swallowed, it transforms the worst sourpuss into a cheerful singing and dancing contemporary. The success is astounding, as is the response in the international media. The pill produces satisfied tax officials, happy drivers, cheerful police officers and smiling burglars. Tourism flourishes, as a trip to Allegretto soon becomes more popular than a vacation in Hawaii. But dark clouds gather over the dwarf state when Field Marshal Heinz mobilizes his troops in neighbouring Moderato.