Maite discovers that the investigation at the Arsenal is full of dark spots and secrets to be revealed. For his part, Tomás has finally found a case that stimulates him: a crime that is about to expire after twenty years.

Tomás and Maite's investigations cause their relationship to suffer, and Maite begins to wonder if she is making a mistake by staying so close to him.

Tomás and Maite discover that not everything is what it seems in the cases they investigate. The past of the suspects and the victims make them doubt every step they take.