Detective Sergeant Timo Harjunpää takes on a strangely elusive case in this mystery that begins with reports of a nocturnal visitor who tiptoes through apartments in Helsinki. Nothing is stolen or destroyed, but numerous women have awakened to an unknown presence in their bedrooms, only to assume in the light of morning that it was all a dream. The police take little notice at first, and the women themselves begin to doubt their sanity. As the evidence accumulates, the dragnet starts closing around a local burglary ring's lock-picker. When the suspect falls in love with one of his nighttime victims, Harjunpää thinks his big break has come, but his pursuit falters when he is forced to reassess his own private life.