In the midst of his morning nap, Carl Mørck, head of Department Q, receives a call from a colleague working on the Danish island of Bornholm with information about a local policeman's suicide, which is somehow connected to a cold case. Some years ago, a young woman was found dead, her body hanging high in a tree. This unusual case sends Carl, Assad, and Rose from the remote island of Bornholm to a strange sun worshiping cult. 
This third selection in the Department Q series starts out rather slow. Two brothers are have been kidnapped and are being held in a remote boathouse. One of them manages to write a message in blood, seal it in a bottle, and drop in into the water. After 13 years and a trip from Scotland, said bottle and note lands on Detective Carl Mørck's desk. Large portions of the note had disappeared and it seemed almost impossible for Carl, Assad, and Rose to be able to solve this puzzle, let alone the crime. But solve it they did, and with such a compelling story that it was nearly impossible to put down. There is a passage in this story wherein a young mother is trapped under a pile of moving crates; it was so well written, so graphic that the reader him/herself feels trapped. So far, this has been the best in the Department Q series! A kidnapper who focuses on large families in closed religious communities; he kidnaps two of the children, demands a huge ransom, then kills one of the children and returns the other, telling the family that he is watching them. He will kill them all if reported to the police, which he knows they will be too afraid to do, and this is how the creep makes his living. He moves from town to town changing his appearance and identity with chameleon-like ease. It is chilling and seems nearly impossible for Department Q to resolve.
The second Department Q novel finds Detective Carl Mørck working at solving a two-decade old brutal murder of a young brother and sister. His investigation brings him into contact with a wily homeless woman and some of the most powerful captains of industry in Denmark. How will he and his unlikely team, Assad and Rose, are pulled into an intricate puzzle of a mystery that makes the book very hard to put down.
I turned to this from a Goodreads recommendation after reading The Girl in the Spider's Web, for Jussi Adler-Olsen is a Danish author who writes intricate mysteries, just as Steig Larsson did. This was a worthy choice. It introduces Carl Mørck, a detective who has just survived an ambush in which one of his colleagues is killed and the other is paralyzed. Carl hesitated a moment and did not draw his weapon, so he is wracked with guilt; the last thing he expects is a promotion, but the promotion to Department Q is really to get rid of him. It is a department of one, save the Syrian immigrant who is assigned to clean, but there is much more to Assad than initially meets the eye. Carl is assigned very cold cases, which no one really expects him to solve, but then they didn't really know Carl Mørck.