1990. Under the glow of a full moon, a sadistic murder is committed on Nordkoster island - a young pregnant woman is buried in the sand, so that she slowly drowns as the tide rises. 25 years later, the case remains unsolved. Olivia Rönning is assigned the case to work on, as cold-case training at the Police Academy. Olivia becomes obsessed with the murder when she discovers that her father, who died several years ago, worked on the original investigation. She soon realises that she has to find the lead investigator, detective Tom Stilton.