In this fifth season, a new elite officer, Anna Gori, arrives at Precinct X Tuscolano, where she will team up with Luca Benvenuto. Meanwhile, a Carabinieri captain, Davide Rea, played by Giampaolo Morelli, tries to gain the trust of Commissioner Corsi and investigates the shooting that left Inspector Belli's wife, Germana Mori, injured and in a coma.
On her thirtieth birthday, Commissioner Giulia Corsi finds herself facing yet another difficult case: three criminals with criminal records for armed robbery are preparing a big heist. The traffic police will discover them during a routine check, in which two police officers will be killed. The intervention of the charming Commissioner Turchi, who has been on the trail of the three criminals for some time, is crucial to the investigation. Just recovered from the serious wound inflicted by Turchi, Giulia returns to the X Tuscolano. Mauro and Roberto are investigating an unidentified young woman who was hit the night before and kept in a pharmacological coma. They find her car and from there they discover that Flavia is the wife of a well-known jewelry designer, Guido Palmeri. Once in his atelier they find themselves in front of the artist's body, killed by a stab to the heart.
The boy who saved Sabina by taking her to the hospital for an emergency birth shows up at the Corsi sisters' house to say hello: Giulia thanks him, Sabina invites him to Paolo's baptism. Mauro and Roberto chase two robbers who have just robbed a jewelry store: the fugitives run over an elderly man, forcing the officers to stop. From an image taken by the jewelry store's video camera, the new arrival Anna discovers a scarification on the criminal's wrist. Seventeen-year-old Elisa, found on the street in a state of shock, is taken to the X Tuscolano: the girl says she was beaten and raped at the home of a boy she met the night before at a disco. Matteo Socci, the classic daddy's boy, reacts with mockery to Elisa's accusations, denying everything.
Mauro wakes up on the beach in front of the villa where Germana had arranged to meet him the night before. He is drunk, he doesn't have his service pistol and he has been hit in the head. At home he discovers Germana in bed with the man from the hotel, both in a pool of blood. Captain Rea's carabinieri arrive: shortly after, Commissioner Corsi and Roberto, Giulia recognizes him as the man who saved Sabina. Mauro follows Germana to the hospital: the woman is seriously injured, the man is dead. While Anna and Luca investigate the case of a girl killed in the night by a hit-and-run driver, Roberto receives confirmation from Boni that Mauro's gun was recently fired. The policeman is tormented by doubt: what if his best friend was really guilty? Meanwhile, social worker Marina Stopponi decides that little Pietro must return to the institution. Mauro tries to oppose but the child is angry with him because he lied to him about Germana.
Mauro is detained at Forte Boccea, the press splashes the monster on the front page. Roberto continues to investigate and learns from the caretaker of the villa that Liverani did not have a license: if he was not the one who drove Germana's car, the hypothesis of the presence of a third man and of the staging to frame Mauro becomes certain. In the meantime Giulia, Luca and Anna deal with the kidnapping of twenty-year-old Gabriele Mattei. After being released from prison, Mauro rushes to Germana's bedside, still in a coma. He then returns to the X Tuscolano, celebrated by his colleagues, and with Roberto he follows the case of a woman who was found lifeless by her son, inside her apartment. Giorgia Morelli was the victim of a loan shark in the area, Taddei, who according to her son could be the murderer. Giulia will discover that the woman, desperate about her situation, actually committed suicide.
Captain Rea and the district team continue their investigations to discover the perpetrators of the Liverani crime. Thanks to the identikit provided by Germana, they manage to trace the identity of the murderer: it is a man who worked for the secret services in Somalia. When Luca and Anna track him down, they just have time to save him from a deadly ambush. In the meantime, Giulia investigates the case of a young man found dying after ingesting a deadly cocktail of narcotics. A friend of the victim reports the dealer who is supposed to have sold the drugs. Mauro and Roberto investigate the death of a beautiful woman of Slavic origins, with a past as a prostitute, who, moreover, was pregnant. It will be discovered that the victim was hiding a double life from her husband. Why was she lying to her husband? Behind the bitter story, the agents will come to reveal a tragic truth.
After the failed attack on Terenzi by the two mysterious motorcyclists, all that remains are the bullets from the shooting. Parmesan and Rea work together to discover that Terenzi's gun had already been fired two years earlier to kill a city councilor. Meanwhile, Mauro and Roberto are dealing with the case of a twenty-year-old drug addict found dead in the Colle Oppio park. Her policeman brother, Stefano, is convinced that the killer is the drug dealer Sanna and demands to participate in the investigation. While Roberto and Mauro are dealing with a thief called Fantomas for his extraordinary disguises, in the guise of a priest the man has stolen a gift from Roberto's house intended for Francesca, returning that evening, Anna and Luca follow the case of a young swimming champion attacked after a training session, in the darkness of the locker room. Viola has a bad fracture in her arm and will not be able to participate in the European championships.
Thanks to the joint investigation of the Police and the Carabinieri, Giulia and Davide discovered twelve tons of drums containing toxic and carcinogenic waste hidden in the land purchased with the mediation of the broker Liverani and cost the life of a city councilor killed with Terenzi's weapon. Germana writes an article on the ecomafia that is published on the front page and sparks a great debate. From that moment on, Terenzi follows her insistently. The two officers of the X Tuscolano will discover a fierce baby gang that terrorizes the institute by stealing the scooters of the students who are then beaten to force them not to file a complaint. The vehicles are then received by the young janitor and Bruno, the aspiring leader of the gang.
Mauro tells Giulia that he suspects there is a mole among the Carabinieri, but the commissioner thinks he is too involved and passes the investigation to Luca and Anna. Agent Gori collaborates with Captain Rea in the search for the CD-ROM that Liverani wanted to give to Germana, but nothing happens at the villa. Roberto and Mauro instead deal with the case of a newborn baby kidnapped from a clinic: they will discover that it was the very young natural mother, the Albanian Irma, who took him back. In fact, the baby was sold to a wealthy childless couple. Daniele, Sabina's brilliant computer scientist partner, is involved by Mauro in the investigation into the ecomafia: his help is needed to decrypt Liverani's CD-ROM. Giulia decides to cover for her men, unleashing the ire of prosecutor Altieri who had assigned the investigation to the Carabinieri. Davide is also hurt by Giulia's choice but she explains her doubts to him.
Roberto and Luca investigate Maroni, a prisoner who escaped from his prison guards to prepare a robbery at a post office and leave with his partner Nadia for the Philippines. The woman, suffering from a serious breast tumor, hopes to be saved by a local healer and for this reason Maroni, stopped by the officers, locks himself in the place threatening to kill the hostages if they don't give him a car to the airport within an hour. Cristina Bini, a young babysitter, is stabbed to death by her ex Carlo Serra, a drug addict who stole her three-year-old daughter, Laura, who was with her. The little girl is the daughter of Lieutenant Nicola Riva, a colleague of Captain Davide Rea who is taking part in the search. Serra is found in the farmhouse where Paolo Libero was killed for the investigation into pedophilia and confesses to having given Laura to a stranger.
Two young, unwary men, Chicco and Spillo, rob the junk shop of a certain Politi, who is actually a dangerous fence who in fact reacts by shooting at the fleeing motorbike and hitting Spillo. Roberto, Luca and Anna collect Politi's complaint, later discovering that the man reacted in this way because the two had stolen some precious jewels from him, hidden among the junk. While Luca and Anna investigate the murder of a man who has just been released from prison after a rape conviction, Mauro expresses his anger to Giulia over Bondi's disappearance: the agent is convinced that the mole is Captain Rea himself. The commissioner is torn between his attraction to the man and Belli and Ardenzi's legitimate suspicions about the investigation into the ecomafia. Mauro and Roberto track down Bondi's acquaintance, Giacomo De Gregori, the owner of a transport company that received a lot of money from Liverani.
Mauro and Roberto deal with the case of criminal lawyer Paolo Silvestri, killed by one of his former clients, a criminal who had just been released from prison. The two agents track down Panessa's hideout but there they discover the man's body with his head smashed in and twenty thousand euros in his pocket. They will discover that Silvestri was divorcing his wife Lucia, also a lawyer who now shares the office with her colleague Bruno Cattaneo, her lover. While Davide and Giulia wait in the hospital for Giuseppe Castaldo to wake up, miraculously alive after being wounded by Rea, Francesca and Roberto discover that the woman is pregnant. Mauro and Roberto follow the captain in the inspection of the house burned by Castaldo where Mauro discovers the fragment of an article in English that he gives to Germana to trace its origin: the photo shows Nina's face.
Mauro shows Roberto the photo from Somalipress that portrays the young Davide Rea with Nina, Terenzi and Castaldo. The two rush to Giulia's house where they discover that the captain spent the night there. Forced to remain silent, they ask Altieri to interrogate Castaldo again but when they arrive at the hospital the man has already been killed. They show the photo to Giulia who is shocked. Meanwhile, Luca and Anna investigate the disappearance of a beautiful dancer who came from the province to make her fortune. Giulia seems to have fallen into a deep depression: she cannot accept the truth about the man she loves. In the meantime, Luca has arrested the drug dealer Nardi, who has sent his protégé Damiano to the hospital, beating him bloody. At the police station, while Luca is interrogating him, Nardi collapses and dies. The officer is suspended and investigated by two disciplinary inspectors for homicide.
While Roberto and Mauro investigate the case of an artist who disfigured two young people with a solvent used in painting, Giulia interrogates Lieutenant Riva, suspected of complicity in covering up the disappearance of Captain Rea. The carabiniere firmly denies his involvement and the commissioner decides to have Luca and Anna follow him. Roberto and Mauro will be able to reconstruct the delirious plan for revenge of Rinaldi, the painter whose wife lost an eye due to a beer can thrown from an overpass while their car was in transit. With Giulia's help, they will save Daria, the last girl suspected of the act by Rinaldi, who will be arrested. Meanwhile, Luca and Anna continue their search for Captain Rea. Rea shows up with Giulia, making an appointment at the amusement park. It's the moment of truth, to reveal what's really happening. The entire 10th Tuscolano is ready for the final showdown.
Mauro and Roberto investigate the beating of sixteen-year-old Bruno Cordari, which took place in front of his high school: the boy is in intensive care. The two officers of the X Tuscolano will discover a fierce baby gang that terrorizes the institute by stealing the scooters of the students who are then beaten to force them not to file a complaint. The vehicles are then received by the young janitor and Bruno, the aspiring leader of the gang, who in competition with Andrea Moretti, a classmate of his who becomes the main suspect. But the story is even more complex. Meanwhile, Germana has been summoned by Terenzi for an interview: the former para' feels in danger and wants to tell her everything he knows.
Mauro tells Giulia that he suspects there is a mole among the Carabinieri, but the commissioner thinks he is too involved and passes the investigation to Luca and Anna. Agent Gori collaborates with Captain Rea in the search for the CD-ROM that Liverani wanted to give to Germana, but nothing happens at the villa. Roberto and Mauro instead deal with the case of a newborn baby kidnapped from a clinic: they will discover that it was the very young natural mother, the Albanian Irma, who took him back. In fact, the baby was sold to a wealthy childless couple: but the child is ill and Roberto will convince Irma to have him treated. This story will make him understand how much he cares for Francesca and how much he wants to have a child with her.
Daniele, Sabina's brilliant computer scientist partner, is involved by Mauro in the investigation into the ecomafia: his help is needed to decrypt Liverani's CD-ROM. Giulia decides to cover for her men, unleashing the ire of prosecutor Altieri who had assigned the investigation to the Carabinieri. Davide is also hurt by Giulia's choice but she explains her doubts to him. In the meantime, Anna and Luca confront each other on a delicate family case: eleven-year-old Stella accuses her stepfather of having molested her; in reaction, the girl's father brutally attacks his wife's new partner, who in the end turns out to be innocent. Anna confides in Luca that at the same age as Stella she was raped by her stepfather. Meanwhile, Terenzi's two murderers show up at the X Tuscolano disguised as Carabinieri demanding the CD-ROM.
Roberto and Luca investigate Maroni, a prisoner who escaped from his prison guards to prepare a robbery at a post office and leave with his partner Nadia for the Philippines. The woman, suffering from a serious breast tumor, hopes to be saved by a local healer and for this reason Maroni, stopped by the officers, locks himself in the place threatening to kill the hostages if they don't give him a car to the airport within an hour. Rea tries to understand what happened at the X Tuscolano with the two fake carabinieri who stole Liverani's CD-ROM. Altieri is furious about what happened and takes the case away from Giulia: Rea, however, promises her that they will continue to work together. Parmesan is in shock after an accident.
Cristina Bini, a young babysitter, is stabbed to death by her ex Carlo Serra, a drug addict who stole her three-year-old daughter, Laura, who was with her. The little girl is the daughter of Lieutenant Nicola Riva, a colleague of Captain Davide Rea who is taking part in the search. Serra is found in the farmhouse where Paolo Libero was killed for the investigation into pedophilia and confesses to having given Laura to a stranger. Giulia confronts Pietro De Santis, the former criminologist in prison for child trafficking: the monster, in exchange for lifelong isolation, names Alfredo Castiglia, in whose house Laura is found, safe and sound. Giulia faces her past and Paolo's death, Rea is close to her.
Two young, unwary men, Chicco and Spillo, rob the junk shop of a certain Politi, who is actually a dangerous fence who in fact reacts by shooting at the fleeing motorbike and hitting Spillo. Roberto, Luca and Anna collect Politi's complaint, later discovering that the man reacted in this way because the two had stolen some precious jewels from him, hidden among the junk. The case will be solved with the collaboration of the informant Camomilla, who reveals herself to be Chicco's uncle, and thanks to Roberto's timing who manages to save the two from Politi's retaliation. Meanwhile, Parmesan brings the note found on Nina's tombstone to Mauro's house: it is a clue, albeit a weak one. Giulia suggests that Rea have Mauro help her in the investigation.
While Luca and Anna investigate the murder of a man who has just been released from prison after a rape conviction, Mauro expresses his anger to Giulia over Bondi's disappearance: the agent is convinced that the mole is Captain Rea himself. The commissioner is torn between his attraction to the man and Belli and Ardenzi's legitimate suspicions about the investigation into the ecomafia. Mauro and Roberto track down Bondi's acquaintance, Giacomo De Gregori, the owner of a transport company that received a lot of money from Liverani. When questioned, the man admits to having transported toxic waste on behalf of the broker and eventually gives up Bondi's cell phone, which turns out to be a false name. At that moment, Rea bursts into the X Tuscolano, furious at not having been warned of the developments in the investigation.
Mauro and Roberto deal with the case of criminal lawyer Paolo Silvestri, killed by one of his former clients, a criminal who had just been released from prison. The two agents track down Panessa's hideout but there they discover the man's body with his head smashed in and twenty thousand euros in his pocket. They will discover that Silvestri was divorcing his wife Lucia, also a lawyer who now shares the office with her colleague Bruno Cattaneo, her lover. The man had exploited Panessa's hatred to have Silvestri killed, of whom he was jealous, only to then also kill the murderer who asked him for more money. In the meantime, Parmesan has tracked down the address of Nina's partner through the cell phone given by De Gregorio: Giulia, Mauro and Roberto prepare a raid on the villa but the man has already been warned.
While Davide and Giulia wait in the hospital for Giuseppe Castaldo to wake up, miraculously alive after being wounded by Rea, Francesca and Roberto discover that the woman is pregnant. Mauro and Roberto follow the captain in the inspection of the house burned by Castaldo where Mauro discovers the fragment of an article in English that he gives to Germana to trace its origin: the photo shows Nina's face. Francesca is robbed by a drug addict who pricks her with a possibly infected syringe: after much research Roberto and Mauro manage to catch the thief who fortunately turns out to be HIV negative. Meanwhile Luca and Anna deal with the case of a young gay man beaten to death in his own apartment, perhaps by his gym mates who had discovered his diversity.
Mauro shows Roberto the photo from Somalipress that portrays the young Davide Rea with Nina, Terenzi and Castaldo. The two rush to Giulia's house where they discover that the captain spent the night there. Forced to remain silent, they ask Altieri to interrogate Castaldo again but when they arrive at the hospital the man has already been killed. They show the photo to Giulia who is shocked. Meanwhile, Luca and Anna investigate the disappearance of a beautiful dancer who came from the province to make her fortune: they will discover that Cinzia was on the eve of an important job that turned out to be an illusion; furthermore, disappointed by her best friend who stole her boyfriend, she chose to take her own life. Meanwhile, Rea understands that the boys of the X° Tuscolano have discovered something that concerns him closely.
Giulia seems to have fallen into a deep depression: she cannot accept the truth about the man she loves. In the meantime, Luca has arrested the drug dealer Nardi, who has sent his protégé Damiano to the hospital, beating him bloody. At the police station, while Luca is interrogating him, Nardi collapses and dies. The officer is suspended and investigated by two disciplinary inspectors for homicide. The autopsy confirms the head trauma as the cause of death but Francesca explains that the trauma can be older than 24 hours and manifest itself late with a sudden death. The colleagues will have to prove Luca's innocence in a short time also with the help of Giulia and the lawyer Sergio Premoli.
While Roberto and Mauro investigate the case of an artist who disfigured two young people with a solvent used in painting, Giulia interrogates Lieutenant Riva, suspected of complicity in covering up the disappearance of Captain Rea. The carabiniere firmly denies his involvement and the commissioner decides to have Luca and Anna follow him. Roberto and Mauro will be able to reconstruct the delirious plan for revenge of Rinaldi, the painter whose wife lost an eye due to a beer can thrown from an overpass while their car was in transit. With Giulia's help, they will save Daria, the last girl suspected of the act by Rinaldi, who will be arrested. Meanwhile, Luca and Anna continue their search for Captain Rea.
Rea shows up with Giulia, making an appointment at the amusement park. It's the moment of truth, to reveal what's really happening. The entire 10th Tuscolano is ready for the final showdown.