Forensic pathologist Sara Grau is called to the scene of a car crash in which a man and a woman have died. While performing an autopsy on the man's charred body, Sara recognises a distinctive tattoo.
Following a series of brutal murders of elderly women, the police are searching for a man dubbed The Granny Killer who has just claimed a fourth victim. Judge Fermi Cases is asked to lead the inquiry.
Sara aims to find out more about the burnt car crash victim. She visits his widow and discovers he has a connection with her own lover, who bears the same tattoo: they served in the army together.
The police have identified firefighter Marc Ramos as a prime suspect, but just as his next victim is lined up, a twist sees him hailed as a hero for saving her life. Cases asks his wife for a divorce.
Under mounting pressure to show progress in The Granny Killer investigation, Judge Cases releases the CCTV footage of the man police believe to be the culprit, but it backfires spectacularly
Sara is followed on her way to work, and back home again in the evening. She confronts her lover and asks him to leave her alone. Feeling cornered by his wife, Judge Cases makes a drastic decision.
Merce, the wife of Judge Cases, is unaware that her husband, who is in Majorca with his mistress Magda at a conference, has set in motion plans to have her killed by local police informant Fajardo
Detectives Sonia Silva and Toni Guillen have questions for Judge Cases about his wife. Marc Ramos hears news of a copycat killer and is perplexed. He heads out into the night to claim his next victim.
The police find a clue in the shape of a footprint, but are puzzled that the latest victim's profile doesn't fit the pattern of the others. An image on the TV leads Sara to a shocking realisation.
Now aware that Marc Ramos is her nameless lover, Sara tries to find out more about him. Her investigations lead to a soldier named Victor who served with him in Iraq. Fajardo blackmails Judge Cases.
At the police station, Ramos is confident that his mother will give him any alibi he needs and he submits to a DNA test that puts him in the clear. Judge Comas is forced to release him from custody.
Ramos continues to make Sara's life a living hell, and the press depict her as a vengeful and unfaithful woman who has unfairly accused a heroic firefighter. The net closes in around Judge Cases.
Sara confronts Ramos's mother with evidence of his crimes, insisting that she is protecting a monster by providing her son with an alibi. But when Sara heads home, she finds herself in mortal danger.