On a beautiful summer day in Sandhamn, children are playing hide and seek in the woods when one of them makes a gruesome discovery: a human arm in a bag. Mia and Thomas investigate and make a connection to the disappearance of a girl a year earlier. Doctors confirm this to be the case. Thomas is busy with the investigation, but finds time to take his ex-wife to dinner.
When a second girl is reported missing in Sandhamn, and her bike is found on a cliff, many fear the worst so the police, accompanied by volunteers, begin a search. Has she been murdered? Nora finds a clue and also discovers that Thomas has met his ex-wife so lets herself be courted by sailing teacher Magnus.
Who hit Mia on the boat to Sandhamn? Is this the same person who is responsible for the disappearance of the two girls? Goran, Lena’s father, is questioned but Thomas and Mia now doubt his guilt. Meanwhile human remains are discovered once again, and a new investigation is launched by the police. This fatal discovery allows them to find some interesting things, but the key to the riddle lies in the notebooks under Nora’s bed.