In the fourth series involving the Danish National Police's elite mobile "Unit One", personal issues have begun to wear on the team's performance. Chief Ingrid (Charlotte Fich, HEADHUNTER) continues to balance work, family - especially with her mother overriding her punishments for her son who is still acting out after the brutal murders of his uncle and cousin in the third series - and relationships (including recurring pathologist Boysen [Michael Falch, APPLAUSE]). Profiler La Cour (Lars Brygmann, THE CELEBRATION) has doubts about whether he will make a good father, and is also unnerved by how vividly he can slip into the mindset of killers. Fischer (Mads Mikkelsen, THE HUNT) is dealing with his divorce, custody issues, and his new relationship with a fellow officer (who called off her own wedding). Ingrid's second-in-command I.P. (Waage Sandø) is still dealing with his wife's alcoholism and her affair with his superior Ulf (Erik Wedersøe, Van Trier's IDIOTERNE). Information officer Gaby (Trine Pallesen, LITTLE BIG GIRL) and driver/soccer star Johnny (Lars Bom, PUSHER) are attempting to move past her miscarriage and his dalliance with a prostitute by getting married.

In the first episode, Ingrid and La Cour are called in to verify the ascertained sequence of events in the case of a grandfather who killed his daughter, his granddaughter, and critically injured his wife before turning the gun on himself. La Cour pokes holes in the scenario and surmises the presence of an intruder familiar with the skeletons in the respectable family's closet. Ingrid's preoccupation with her mother's relationship with Ulf during her childhood (and possibly before) has her overlooking the most likely suspect. The second case takes things into STRANGERS ON A TRAIN territory when a philandering fishmonger comes home from Paris to find his wife - co-owner of his business - brutally murdered, seemingly the latest victim in a series of robberies. The unit examines the scene and realizes that it looks more like a hit designed to look like a robbery. The not-so-grieving husband suspects that it has something to do with the frank conversation about his marriage that he had with a flamboyant fellow traveler. Fearful of being charged with complicity in a murder he never wanted, will he seek the help of the unit or reluctantly follow through with his end of the bargain? Things get personal for Ingrid again in the third episode when the niece of a colleague is believed to be the latest victim of a murderous rapist until pathologist Boysen says otherwise. Since the killer's method of trinket-collecting from his victims was never disclosed to the press, the unit realizes that the killer must be one of their fellow officers.

When Johnny stumbles upon a refrigerated truck with two women (one dead and one critical) trapped inside, the unit faces off against a human trafficking organization with deep pockets in the fourth episode. When La Cour discovers the body of a missing student at the Soro Academy in the tense fifth and sixth episode two-parter, the team realize that they might have solved the case of Denmark's only serial killer when they find incriminating evidence in the student's room. They soon realize that the killer may still be loose when he targets Gaby. Meanwhile, Ulf has learned of the government's plan to disband Unit One. The seventh and eight episode two-parter switches over to a longer format as the disbanded Unit One are called back together when the minister of justice is implicated in the murder of an HIV-positive African prostitute. I.P. returns from retirement, Gaby and Johnny return from the road, and La Cour is reluctantly called back from a case involving bikers and a bank robbery. Fischer, on the other hand, has been in jail for six months for selling confiscated amphetamines to the biker gang, but he may be able to offer outside help; ears are everywhere however, and more than one member of the unit may be in mortal danger from the very people they are protecting. The last episodes of the series are certainly full of suspense, but a little disappointing in the way they've left several open ends (possibly in anticipation of a fifth series or possibly another extended two-parter special), leaving one pining for the earlier series when the group operated as a well-oiled machine and only had to worry about their own personal issues.