Faced with their toughest case yet, made only more difficult with COVID-19 restrictions and the challenges of their own personal lives, Department Q, led by Detective Carl Mørck, investigates a series of “accidental” deaths over the span of 30 years that may be the work of a violent serial killer.

A group of survivors navigate trauma and recovery challenges in the aftermath of a mass shooting at a mall, an event that inspires a career in law enforcement, triggers devastating PTSD and gives way to an escaped killer's plot to orchestrate an event with an even higher death toll.