Madrid, 1981. The scene is a wasteground surrounded by old buildings, and inhabited by drug-addicts and tramps of all kinds. A pair of drug-addicts is suddenly put in the sight of two cops, who pursue them in their car... only to reveal in the end that they are informers for the most veteran of the cop duo, Cowboy Cop Jesús Méndez "Pacino" (Hugo Silva). As Pacino and his partner put on a show of arresting the informers, they receive a warning of shouts in a nearby building. Pacino and his partner rush to the address (leaving the drug-addicts handcuffed) and Pacino goes first, telling the other cop to call for reinforcements. When he enters the flat from where the shouts come from, he is ambushed and struck almost senseless by a man who takes Pacino's gun and uses it to kill the woman who lives in the flat with her son. The killer then proceeds to get into a wardrobe and disappear, much to Pacino's shock: he seems to recognize this. Pacino follows with his spare piece and appears in a bar's basement, where he is arrested by two policemen. When Pacino tells them to check his credentials, the policemen laugh at the fact that he thinks they will trust someone with credentials from the 1980s, while Pacino sees on the TV the crowning of King Philip VI.
Word of this event reaches the Ministry of Time, who arranges Pacino's transfer of custody to Salvador, who proceeds to interrogate Pacino. After finding out that he is in the future, and that the papers of his time accuse him of the murder he saw, Pacino reveals that the reason he knows so many details about the place because, in 1946, his father (also a cop) answered to warnings about a murder taking place in the exact same flat Pacino went to. He could not stop the murderer from killing a woman (also a single mother), and, when the murderer got into the wardrobe, Pacino's father was shocked when he disappeared. This led to his disgrace (as his partners, for obvious reasons, never quite believed what had happened) and, later, his suicide. As it is obvious that there is time-traveling shenanigans involved, the Ministry takes charge of the investigation, and Pacino requests to collaborate, wanting to put an end to the murderer.
Amelia, Alonso and Ernesto take charge of the investigation: their research leads to them finding Pacino's gun thanks to a camera that also filmed the murderer, which Pacino easily identifies. Further investigation takes them to their objective, a man called Francisco Morán who, curiously, owns the building where the two murders (and many more, as Irene finds out) happened, and who has also become quite rich. Laying out a trap, Morán is captured and arrested.
Morán reveals that he discovered the time-traveling wardrobe by accident: he comes from 1886, where, as a child, he witnessed to his father's brutal murder of his mother from within the wardrobe, which he closed when his father tried to get him out - then finding himself about fifty years later in time. When he became of age, he was able to use the wardrobe to go back and forth in time, using his foreknowledge of winning lottery numbers and soccer results to earn a lot of money, which he used to buy, among other things, the building where he lived (in fact, the flat where the murders have been taking place is the same one where he lived as a child), as well as fund the orphanage that took him in, and which also took in all the children he orphaned.
Morán then makes a request of Pacino: should he kill Morán's father, then he would be able to prevent all the murders from taking place. Salvador tells Pacino that they cannot change history, so he better forget the idea, but he also welcomes Pacino to the Ministry as a full-time agent, since they now can clean Pacino's name. The following day, though, while Salvador is ready to send the new trio to 1997 to convince Pau Gasol to leave his medicine studies and dedicate himself to basketball, they find out that Pacino is nowhere in the Ministry. Alonso and Amelia follow the clues they find to 1946, the night of the murder Pacino's father could not stop, but Pacino is not there, and Morán (who obviously does not know them) takes the woman in that time hostage.
Instead, Pacino has gone to 1886, in order to prevent Moran's father from killing Morán's mother. A tense double Mexican standoff happens both in 1886 and 1946. Amelia offers to become Morán's hostage if he will let the other woman go, an offer the killer accepts. However, before Morán can escape to the future with Amelia or Morán's father can do the deed, Pacino kills Morán's father: Morán disappears in 1946, much to Amelia's shock, and all the murders Morán committed are reverted, as Morán never time-traveled to the future.
Salvador gives Pacino a big reprimand for his actions, as the Ministry now cannot tell what will happen to those children that now have not lost their mothers, and perhaps any of them or their descendants could end up doing something that completely changes history. However, Pacino stands by his decision, and there are no more consequences - beyond the fact that Pacino's father does not kill himself and, instead, gifts his gun to Pacino when he becomes a cop.
In the meantime, Irene has been looking up any information that may lead her to knowing where Julián is, and finally finds a photograph where he appears in the War of Cuba at the end of the 19th Century. Instead of telling this to Salvador, though, she goes to Susana Torres, who thanks her, because this is but another step towards the Ministry both of them want.
