After an ugly streak of bad luck Franco Montero is forced to adopt his 10 year old brother (who happens to be a child prodigy). With his help, Franco solves an unbelievably complex locked room mystery.
Franco has 2 problems to solve, a sniper kills 3 victims and the visit of a inspector that wants to take Lorenzo with another family. Franco also knows Sanji, Serrano's nephew & new member of the brigade.
A man appears dead with a knife in chest, 4 family declared guilty their selves and later innocents, nobody knows, not even Lorenzo, who is responsible. They are missing an clue that involves a fifth suspect.
Lorenzo, Franco, Mancilla and Sanji are witnesses of a murder during a theatre function when the actors are using a real weapon, they have to know if the responsible are one of the actors or if its an accident.
Lorenzo is sad because other children always are bothering him, they invited him to a costume party but he doesn't know if he should go. Franco has to solve the hardest mystery but this time Lorenzo can't help him because his depression.
Someone wants to kill Serrano and everybody think that was Frantco who shot him because he is in love with Serrano's ex-girlfriend. In this case, Franco, Lorenzo and Mancilla discover a network of corruption of their boss.
Serrano hires an assassin named Darío to kill all who knows about his secret, including Franco. Darío kidnaps Lorenzo as a trap to kill Franco. Serrano is in the hospital, but apparently his health state is normal.
Serrano escapes from the hospital. Franco is the new commander but this work is too difficult. Lorenzo has an opportunity to study in an important school, but this means that he needs to live in another city, away from his brother.