After the disappearance of a 17-year old girl, Det. Sarah Linden investigates the incident, while the girl’s parents search for her, whereupon her body is found in a sunken truck that apparently belongs to the campaign of Councilman Darren Richmond, who’s running in the mayoral elections.
Det. Stephen Holder joins Det. Sarah in the investigation of Rosie’s murder. They question her schoolmates and Councilman Darren Richmond, whereupon Holder finds out about a place in the basement of Rosie’s school called ‘the Cage’, where the crime may have been committed.
With news of Rosie’s murder leaked to the press, Richmond’s campaign is put in an unenviable situation. As Linden and Holder question the suspicious janitor, he tips them off to another suspect. Meanwhile, Rosie’s parents struggle to cope with her death.
Linden and Holder find a new lead, but it turns out to be useless. While searching Rosie’s bedroom, Linden finds new clues that prove interesting. Rosie’s grieving parents start making the arrangements for her funeral. Richmond’s poll numbers continue to plummet.
As a clue leads Linden and Holder to Bennet Ahmed, Rosie’s teacher, he claims that he’s innocent, but hands them another clue. Rosie’s father, Stan, seeks his colleague’s help to find the killer. Richmond’s team decides to air anti-crime ads to help improve his image.
The Larsens hold Rosie’s funeral. As new evidence surfaces, Bennet Ahmed becomes the prime suspect, whereupon Stan decides to take action. The debate between Richmond and the current mayor doesn’t go well for the former.
Linden grapples with a personal problem. Stan attempts to take revenge on Ahmed, whose wife reveals new information in the case. Richmond rejects the idea of asking Ahmed to step down from his position in the former’s community project, which, in turn, has an adverse effect on his image.
Linden and Holder run into problems with their investigation that threaten its fate; meanwhile, Linden struggles in her relationship with her fiancé and her son. Richmond deals with old personal tragedy, while continuing to come up with tactics for his campaign. Stan and Mitch’s relationship turns sour.
Darren Richmond makes an important decision regarding his campaign. As the police’s attempt to arrest Ahmed fails, they discover something startling; meanwhile, the Larsens grow tired of the police’s irresolution.
The police are tipped off to a new suspect in the case, as the investigation into it recommences. Richmond’s team finds out something puzzling about him. Stan’s foolhardy actions cause him trouble, while Mitch is left to take care of the family.
The murder investigation is put on hold, as Linden’s son, Jack, goes missing, forcing her and Holder to search for him.
As the investigation continues, the police find a link between Rosie and a shady website. Mitch Larsen learns some shocking information. Richmond’s poll numbers go up, while his opponent’s slide.
The police unearth compelling evidence in Rosie’s case, which further suggests Richmond’s involvement with her. As the Larsens face another tragedy, Stan and Mitch contemplate the future of the family.