A quiet Sunday in Rome... for the police officers of the Mobile Squad, however, Sundays, like the rest of the days, are never quiet. This Sunday in particular, everything happens. It would be Ardenzi's birthday but between stalking, drug trafficking and women who want to throw themselves into the Tiber, the day seems to never end. The Mobile Squad is dealing with a typical day at work in the Capital. An old friend of Ardenzi, a well-known restaurateur in the historic center, turns to the commissioner to solve a problem with his son. Meanwhile, a young girl who is not yet of age is taken to the police station together with the man who lured her.

Zaccardo, head of the Section, informs Ardenzi and Sabatini of an upcoming very important operation to capture a fugitive in a Roma camp in the Capital. They must prepare and carry it out as best they can. This obviously while emergencies arrive at the Police Headquarters. Today is the day of the blitz. The team is finalizing the final preparations but the police headquarters receives a report of a woman run over on Lungo Tevere, and moreover the daughter of a repentant.

While at the police station Claudio Sabatini is looking for a way to free Bradic, who is being held awaiting questioning, without arousing the suspicions of his colleagues, Ardenzi and Sandro are dealing with the case of a Pakistani girl stoned to death in the street and Isabella is dealing with her first serious friction with her boyfriend Giulio who ends up slapping her with serious consequences. Bradic's death at the police station and at the hands of Marcello, forces the commissioner to put the young policeman under investigation and for this reason Oliviero, feeling misunderstood and unjustly accused, runs away and disappears. Ardenzi is worried about the boy, he wants to find him and it is his job to clarify the dynamics of the facts; Claudio Sabatini also needs to find Marcello.

The death of Marcello has shocked the entire team but the worst blow was suffered by Roberto who feels responsible for the boy's disappearance and is now determined to understand what happened. In the meantime, Sandro and Giacomo discover a prostitution ring run by chinese where underage girls are enslaved; while Isabella and Valeria manage to save Giulia, a woman mistreated by her husband, who for the love of her daughter finds the courage to report him... but for Isa, a champion of mistreated women, the real troubles begin now: on her PC, in fact, an order to stop from an anonymous but very threatening sender arrives. Ardenzi, following the notice of investigation, appears before the judge with his lawyer and discovers that he is being investigated for incitement to suicide.

Sandro remembers that Marcello had confided in him shortly before his death that he had seen Sabatini in the company of a person who could be Bradic. Ardenzi thus begins to suspect Sabatini. While Zaccardo, having learned from the police chiefs that she will be promoted, has decided to offer her position to Claudio. Sabella is called by Cristina in tears because her partner has returned to her and is threatening her. A drug dealer questioned by Ardenzi in prison accuses Sabatini of being corrupt. Darko Bradic's body is found and Ardenzi is increasingly convinced that Sabatini is involved in this chain of crimes.

Isabella is suspended for beating Cristina's murderer after his arrest. Sandro and Ardenzi follow Sabatini and discover that he is meeting with Lele Bianchi, a customs officer from the port of Civitavecchia already known for previous drug dealing. Zaccardo informs Ardenzi that Sabatini will be in charge of the section. Ardenzi interrogates Lele Bianchi to try to obtain evidence against Sabatini, but before he can obtain any information, Bianchi is released from prison.

Bianchi's body is found, killed by Sabatini and thrown into the river, but there's no trace of the tablet recording the drug trafficking. Claudio, promoted to head of the unit by Zaccardo, plots to have Ardenzi expelled from the station, now at war with his former friend. Ardenzi, with the help of his team, decides to search for the gun used to kill Bradic, which Sabatini may still be hiding in the house. Roberto finally manages to confess to his daughter about her mother's true death, and their relationship grows stronger.

On the day of Valeria's and Zaccardo's wedding, he informs Ardenzi of his transfer to the Viterbo police station. The team therefore has little time to frame Sabatini: they must find the gun that killed Bradic and Clerici as soon as possible and foil the major drug trafficking that Claudio is completing with the help of Vanessa. Sandro finally discovers Sabatini's garage where the gun is kept, but this discovery could be very dangerous. Sandro, seriously injured by Vanessa, is taken to the hospital in serious condition. Ardenzi recovers Sabatini's gun and can finally prove his guilt. Claudio, now hunted, wants to carry out the last drug trafficking and then flee abroad.