It is 1864. Under a full moon, a town sleeps placidly, and in the nearby forest the night animals sound. Then, a woman starts running across the forest, persecuted by men with Torches and Pitchforks and dogs. She manages to hide under the roots of a tree and escape, but falls in a trap, where she is found by a young man who sets the woman free... just in time for the man to wake up and write a letter.
We return to the present, where it turns out that the Ministry intercepted that letter. The young man is the Spanish Romanticism poet Gustavo Adolfo Bécquer
, and the letter is the tenth of what was supposed to be nine, found along with a drawing of a woman who has a surprising similarity to women from a painting from the 16th century and from an engraving of 1687 - which makes them think she might be a time traveler. Their mission is to find the woman, called Mencía, and find out what's going on.
Upon arriving to 1864, the patrol engages in a literary discussion, while two women (one of them Mencía, the other heavily pregnant) appear to engage in a ritual of some kind.
In the present, Salvador requests Irene to do something unusual: to train young Lola Mendieta. Irene is not keen, remembering how old Lola betrayed the Ministry, but in the end she agrees, as long as Salvador accepts her decision over her suitability.
The trio arrives to Trasmoz, passing themselves of as pilgrims going to Zaragoza. Two local people speak of Mencía, claiming she's a witch - and their son is married to the pregnant woman that was earlier with the witch.
In the present, Salvador explains the situation to young Lola, while Angustias clearly demonstrates her anger with Lola, clearly remembering the old Lola's betrayal. Young Lola accepts the offer to work for the Ministry.
In the Monastery of Veruela, Amelia meets Bécquer, whom he asks about the woman in the forest. Bécquer tells her that the locals are superstitious and uncultured, telling her of their murder of an old woman who was said to be a witch. The pregnant woman meets with the witch, who tells her her child will be a boy.
In the present, Angustias tells Irene that she does not agree with Salvador's decision, thinking that young Lola will eventually betray them like her older self. Lola arrives, keen on starting her work, but Irene asks her to detail everything she remembers about Salvador's office, which she does for several hours.
That night, Bécquer is awake, and Pacino speaks with him, wondering what keeps the man awake: Bécquer is worried about the woman. While Pacino speaks with the man, telling him about the supposed shipwreck the three were in (and retelling the story of the Titanic), the witch sneaks in Amelia's and Alonso's rooms and cuts off a lock of their hair, which she later uses in some sort of ritual.
Amelia, Alonso and Pacino part ways on the following day: Alonso helps some men with a carriage, Amelia investigates in the town and Pacino follows Bécquer as he meets with Mencía, telling her she must leave, as the townspeople fear her... and they kiss. Pacino leaves.
In the Ministry, Lola's training continues. After some door visiting, Lola investigates the paintings, and realizes that the eldest of them comes from 1510-11, based on some details. And, most importantly, the difference in years between the paintings is the same: a signal that Mencía may be using a time door.
The townspeople confer about Mencía, fearing her and wanting to kick her out. The pregnant woman gives birth to a baby boy.
In the present, Irene tries to call the patrol, but the call does not go through. Alonso and Amelia seem awfully placid, to Pacino's surprise... and Mencía takes the child away during the night.
The following day, the town is up in arms, and goes out in strength to find Mencía and the baby. Pacino is reluctant to reveal where Mencía is hiding and directs Alonso and Amelia to help while he interrogates Bécquer, but the poet rushes to find Mencía. Pacino attempts to call the Ministry, but Alonso tells him that he accidentally broke it.
In the present, Lola is being subjected to a polygraph, and questioned heavily over her reliability. Lola accidentally gets caught in a lie, and ends up revealing the reason she has been seeking the archives: having noted everyone's hostility, she chose to seek her own history, and found about the actions of her old self. She reassures Irene she does not intend to betray the Ministry, but points out that she thinks it's better to commit a crime while fighting injustice than causing it.
In the past, Pacino finds himself in a trap - and Mencía finds him, carrying the baby. Pacino convinces her to help him, as he can help protect her. During the escape, Pacino accidentally breaks a bottle of milk - and finds a strange piece of paper he takes for himself. Pacino takes her to the monastery, the one place where he is sure they are not going to find her. Pacino returns to the town and asks Amelia where the mother is. After pointing out where she is, one of the townspeople asks Amelia what Pacino wanted - and Amelia tells him not only that he knows where Mencía is, but also that she probably is at the monastery. Meanwhile, Pacino goes to talk with the mother, who dies while he tries to interrogate her - but not before she whispers him something.
The townspeople invade the monastery, but Mencía has escaped just in time, running to the forest. Meanwhile, Pacino meets Bécquer so he will help him protect Mencía. However, that night, it turns out that Mencía has been captured along with the baby... and the townspeople are a Satanic sect that has brainwashed Alonso and Amelia. Pacino and Bécquer rescue Mencía (who tells them she took the baby because the towspeople would kill him) and the baby, but they are heard and they run away. In order to escape, they separate: Bécquer takes the baby, while Pacino distracts the townspeople. Mencía, however, decides to stop running, and, cornered by the aquelarre, she states it's the same thing at every time before jumping to her death. The townspeople proceed to run after Pacino, who escapes by going to the time door.
During the debriefing, it turns out that the piece of paper Pacino found was part of the Libro de las Puertas, a piece that reveals there are two doors in Trasmoz, that take people a hundred and seventy-seven years apart. Mencía was from the 16th century, condemned by the Inquisition for witchcraft, but she escaped and found the time door by accident, which probably led to her believing she had magical powers. The baby will be remembered as Bécquer's son. Pacino asks what they are going to do about Alonso and Amelia: Salvador just sends a bunch of agents to bring them to the present, unconscious. The analysis reveals that the town's waters (which all three of them drunk, but Pacino had them boiled first because of a stomach illness) were drugged: the two of them should get better soon. Pacino hopes that Mencía will be able to find in death the peace she was denied in life.
