The hero of the series "Kriger" is a war veteran named Sisi, who recently returned to his native Denmark after serving in the army. He suffers from a sense of guilt after losing a close friend on one of their last missions. The widow of the deceased, named Louise, serves in the Copenhagen police force. She asks Sisi for a favor - to infiltrate a dangerous biker gang undercover. The members of the gang regularly break the law with serious offenses, but proving their guilt has been impossible. In order to repay his moral debt, Sisi willingly takes on this mission.