blackout leaves the distinguished halls of the Löwanderska Hospital in complete darkness. Doctor Sverker Löwander hears the alarm when one of the ventilators go off, and rushes to the intensive care unit only to find the nurse in charge dead in the stairwell and the other disappeared without a trace. When DI Irene Huss arrives, the only witness claims to have seen Nurse Tekla doing her rounds. There's only one slight problem: Nurse Tekla committed suicide at the hospital sixty years ago.

Overview from themoviedb.org