The Trail of the Thief.

Detective Martin Gale, tough with criminals but awkward with women, secretly loves Dorothy Baird, a clever operative at the agency he manages. He gives her a small revolver engraved with his name as a token. Dorothy is assigned to cover a party for a society debutante, where she meets James Vallon, a popular and wealthy young man, and they are attracted to each other. While he flirts with her a valuable necklace goes missing and as Dorothy digs deeper into the incident she begins to suspect Vallon is involved.