As endless summer takes its hold over Stockholm, a different kind of darkness sets in. Clean cut, highly regarded Lead Investigator Thomas Berg has a serial killer on his hands. With the brutal murderer targeting his police colleagues, Thomas makes a desperate gamble, turning to a once well-regarded but now out of favour, misanthropic ex-detective for help. His estranged father, Alfred. If they're to stand any chance of protecting their fellow police officers, they must put their differences aside and find a way to work together. Only then will they catch one of the worst killers in Sweden's history.