The story of Boundless begins when detective Carl Mrck, in a moment of cowardice, sends Rose (his junior colleague in Department Q) to the remote Danish island of Bornholm to answer his old colleague Christian Habersaat’s repeated requests. But during his forced retirement ceremony, Christian kills himself, sending Rose into a journey deep into her own traumatic past. Later, the newly engaged Carl arrives on the island where he, Rose and Assad are embroiled in an old cold case of a girl found dead, hanging in a tree. The killing, officially written up as a traffic accident, has connections to both the local police precinct and a cult of sun worshippers from where young women have been vanishing without trace for years. Once the case is reopened, and the island is now dangerous, Carl must solve it and grapple with his own personal dark past in order to be able to move on and start a new life with his fiance.