Salvador Garrido

Enrique kills a man for stealing him a check he has received due to an accident. However, things get complicated because it had not yet been cashed. This will force him to try to forge the signature and eliminate any suspect, including his girlfriend Clara, who works in a law office and who talked him about the check. Police tracks the case, but by chance Pedrito, the police inspector's son, is also investigating on his own.

An old violin maker has been killed and the investigators have only one clue: on the night of the crime, a blind street musician heard a melody playing in the house. As they do not know the title of the song, they present the music to the famous radio contest known as “The Mysterious Melody”. Little by little the two inspectors will surround the killer after checking that there are several suspects.

After leaving the prison where they have served their sentence, some criminals plan a new robbery.

Duran and his team of the fifth group are secret agents missioned by Inspector Peña to find and capture a gang of dangerous criminals who are planning a major hit.