Aboard the mega cruise ship Sacramentum, 20-year-old new recruit, Jamie, infiltrates the 3000-strong crew in a desperate race to find his missing sister. She was working aboard the same vessel on a previous tour and vanished mid-charter.

Two detectives are dispatched to investigate the murder of a young girl on the outskirts of Dublin, but as the case of the missing children intensifies, both are forced to confront the darkness that lies in their past.