After three Swedish and two Danish youths are found ill on a ship that crashes into Oresund Bridge, Saga is sent to investigate and reunites with Martin, who is still haunted by their last case. They make a disturbing discovery about the youths.

A video is posted online of four individuals wearing animal masks who claim responsibility for the attack. Meanwhile, several deaths are reported as a result of eating poisoned grocery items. Saga and Martin are quick to connect the two cases.

Saga and Martin receive an anonymous tip about the eco-terrorists, who now know the police are onto them. The group continues with their operations but struggle with internal tensions. Martin continues to see Jens, hoping for closure.

Saga and Martin investigate the killing of the eco-terrorists and suspect there is a leader still alive who's been pulling the strings all along. Are there new attacks being planned? Are there more terrorist cells?

A key witness wakes up at the hospital but is suffering from amnesia. Meanwhile, four individuals wearing animal masks carry out a new attack and claim responsibility in an online video. Martin visits Jens again but this time exceeds his authority.

Martin is at the hospital with his son, Nikolaj, who has suddenly fallen ill. When Saga visits, she notices something is off about the place. The case intensifies with another poisoning and the recovery of a suspicious motorboat from the sea.

When someone threatens to blow up a chemical plant, Saga and Martin link all the clues to a common denominator. They pinpoint the perpetrator's location, but will they find what they expect? Martin secretly pries into Saga's past.

Saga and Martin re-interview witnesses and suspect someone within their own group has been doctoring their reports, but need to make sure. Laura finally manages to help piece together a composite sketch of the perpetrator.

With the composite sketch, Saga and Martin learn who the perpetrator is, but can they get to him in time? Just when they think the case is solved, there's one final piece left. Saga and Martin's friendship is put to the test.

Saga and Martin realize the case isn't over and make a discovery about the perpetrator. In a race against the clock to prevent a massive disaster, Martin makes a crucial decision. In the end, Saga faces a difficult choice that will change everything.