A strange nocturnal visitor tiptoes through apartments in Helsinki. Nothing is stolen, nothing is destroyed. Numerous women wake to the unknown presence in their bedroom, but in the light of morning, it all seems a dream. At first the police take little notice, and the women themselves began to doubt their own sanity. But evidence accumulates, and the net closes - Tweety, a skilful picker of locks, falls in love with one of his night-time women. He shadows her, daring to approach her secretly only at night. But then, Tweety's lock-picking skills are needed for a break-in by some of his professional criminal brothers. The results of falling in love and a life of crime are tragic for Tweety. For police sergeant Timo Harjunpaa, times are also hard. He is forced in his private life to reassess his values, the significance of those dearest to him, and the nature of love and guilt.