The arrival of María, the new cleaner, at La Laguna Negra boarding school, after escaping from a psychiatric hospital, will disrupt the peaceful life of Héctor, the charismatic headmaster, who has a seemingly perfect relationship with Elsa, the strict head of studies. A closeness will develop between them that Elsa will try to prevent. María is not the only one fleeing a painful past. Marcos and Paula, after the disappearance of their parents, are taken in by the school under the tutelage of Héctor, who is now their only family.

María finds help after being fired. The girls recognize Alfonso's ring on Marcos' finger.

Marcos discovers a secret entrance in Alfonso's closet, which opens up a whole new world of questions.

Carolina pretends to be Alfonso and sends an email to Ricardo Montoya, with whom she arranges to meet at the cemetery. The journalist explains to the kids the disappearance of the five young orphans in the 1970s and warns them of the enormous danger they face if they continue with their investigation. He insists that they should not trust anyone, either inside or outside the boarding school, but the kids are already too involved in the mystery to give up now. Marcos is worried about his sister, who is too caught up in her fantasy world.

Héctor discovers the mangled corpse of journalist Ricardo Montoya in the lagoon. After recovering from the initial shock, the boys realize that they have lost the only evidence they had of the death of the five orphans. When they return to the well to try to find more evidence, they see that workers are permanently sealing the entrance. They are told that these are orders from the school administration. From that moment on, accidents begin to occur in La Laguna Negra, and the boys realize that the danger they have been warned about is real. Jacinta is depressed. As always, the postman brings back the letters she sends to her daughter Verónica.

The school mystery culminates with the announcement that a student has been found dead in the woods.