Brændt a' (1919)

Every night a common thief stalks the local girl’s school, and he may already have stolen one heart. The headmistress of the school calls upon her nephew, the mighty detective, Basse, to apprehend the thief. On his way, Basse bumps into young Miss Lise, who happens to study at the school. Unfortunately, the great detective fails to grasp the core of the case: that Lise has an undisclosed sweetheart, who pays her secret visits every night after bedtime. (Stumfil.dk)