Hanna, a trained lawyer from Stockholm, has traveled to Dalsland to take care of her grandfather, lock keeper at the 17th lock in the Dalsland canal. A couple of quiet weeks in the country could do her good. However, the harmony she hoped for comes to naught when she realizes that the lock keeper's cabin has become the village's gathering place, where both association issues and village gossip are discussed.

On the big cleaning day, Hanna climbs into her old tree house to escape the intense neighbors, and from her vantage point she witnesses an argument. She sees something flash and how Ulf, the municipal councilor, falls into the sluice shaft.

Everyone except Hanna is convinced that it was an accident, even the police. Desperate that no one is listening, Hanna starts her own investigation, and brings her grandfather along in the search for the truth.

Suppressed conflicts between the neighbors come to light, and there is no shortage of suspects. Hanna becomes more and more convinced that a murderer is on the loose in Södra Strandviken's idyll.

Vatten över huvudet (Water over the head) is the first part of the cozy mystery series Murders at the 17th lock.