Karina arrives to a mansion to work as a governess of a group of singing children. She must take care of their education, and she decides to use music to teach them. Meanwhile, the record company where the children work is busy with another project. Their biggest star, Marta, is getting ready a song to represent Spain in the Eurovision Song Contest 1971. Carlos, the composer of the song, titled "En un mundo nuevo" ("In a new world") meets Karina in the mansion and starts feeling affection to the girl, something Marta, who is Carlos' girlfriend doesn't like at all. She is also jealous of Karina for her musical abilities, and when one day Marta catches Karina with Carlos singing a song composed for the governess, she gives him an ultimatum, if Karina doesn't leave the mansion at once, she will break her contract with the record company and won't sing "En un mundo nuevo" in the Eurovision Song Contest...

Juanito, propietario de una casa discográfica, al tiempo que prepara una canción para Eurovisión que será interpretada por la famosa cantante Marta, ha descubierto a un grupo de muchachos de voces angelicales con un gran futuro. A estos chicos los lleva a su casa, y contrata a Karina, una institutriz que los eduque. Rápidamente, Karina logra el afecto de los niños y el interés de Carlos, prometido de Marta y compositor de la canción de Eurovisión.