Denmark, 2013. Police officers Carl Mørck and Hafez el-Assad, sole members of Department Q, which is focused on closing cold cases, investigate the disappearance of politician Merete Lynggaard, vanished when she and her brother were traveling aboard a ferry five years ago.

Hidden, une ville de Suède en apparence tranquille, est troublée par la convergence d'obscures entités et des forces surnaturelles.