When performing an autopsy on the charred corpse of a car crash victim, respected forensic pathologist, Sara Grau, recognizes a familiar tattoo on the burnt body: it is identical to the tattoo of a man she had a one-night stand with only a few weeks before.

As the Granny Killer follows Sara and Lluís to the hospital and is recognized by Sara as the man she had a one-night stand with, the police discover their first lead. Sara, however, is unaware of her previous tryst's connection to the recent spate of murders in the city.

Figuring out the connection between the car crash victim and her one-night stand, Sara continues to pursue her own investigations, and the police believe they have identified the serial killer terrorizing Barcelona.

A sudden twist sees the chief suspect in the recent spate of killings, firefighter Marc Ramos, being hailed as a hero for saving a woman's life. Meanwhile, Lluís and Clara fly to Tangiers on a business trip together.

The Granny Killer claims his fifth victim and Judge Cases comes under mounting pressure from the public to catch the killer. Performing an autopsy on the fourth victim, Sara notices a strange mark around the victim's mouth...

Unaware that her lover is Marc Ramos, the Granny Killer, Sara confronts him for following her. Meanwhile Judge Cases' wife continues to threaten blackmail, leading him to make a drastic decision.

At his wife's funeral, Judge Cases collapses from a heart attack when questioned about her murder. Meanwhile, Marc Ramos is furious when he hears news about a copycat killer, and heads out into the night to claim his next victim.

When Judge Cases wakes up in intensive care, he is devastated to learn that Mercè was finally going to accept the divorce. Meanwhile, Lluís, feeling angry and rejected at losing his job, forces himself on Sara who firmly resolves to leave her husband. But she is distracted when an e-fit showing on the TV reveals the true identity of the Granny Killer.

As Sara learns more about the dark history of Ramos, her best friend Aitor heads off on a soul-searching journey into the heart of the Basque Country, determined to come to terms with his wife's death.

Ramos is released from custody when his alibi checks out and a DNA test clears him of any involvement in Mercè's murder. Discrediting Sara in the press, he paints himself as an innocent victim of her jealousy.

Ramos continues to make Sara's life a living hell, depicting her as a vengeful and unfaithful woman who has unfairly accused a heroic firefighter of these heinous crimes. Meanwhile, Judge Cases, now back in Barcelona attempts to contact Fajardo. Discovering Fajardo has been arrested again, Cases feels the net closing in around him and makes yet another drastic decision...

When Sara comes into possession of an incriminating video of Ramos torturing a prisoner in Iraq, instead of taking the footage to the police, she first takes it to Ramos' mother in an attempt to make her realize what kind of monster she is protecting.