The mini series is loosely based on actual events involving two of the most active resistance fighters in the Holger Danske resistance group during World War II–Bent Faurschou-Hviid (known as Flame) and Jørgen Haagen Schmith (known as Citron), who both died toward the end of the war. As the two friends exterminate occupying Nazis and Danish collaborators, they also find themselves in deadly duels with treacherous handlers, competing Resistance groups, and a femme fatale who might be a double, or triple, agent. Ultimately, they find that they can only trust one another.