Carl Mørck, the former head of Department Q, comes across a disturbing audio recording and turns it over to his former colleagues, who are struggling to keep the old department up and running on their own. That is, until a new transfer unexpectedly arrives --- Helena Henry, a Frenchwoman who throws herself into the investigation with gusto, but who may also have secrets of her own. When the team realizes that the audio recording might shed new light on a supposedly open-and-shut murder-suicide case from years earlier, suddenly everything they thought they knew is called into question. Meanwhile, a spurt of seemingly random violence leads the Department Q team to investigate a possible connection to a different long-ago dark and sinister event.