"The Unknown" was the final entry in Columbia’s I Love A Mystery series. A woman hires two detectives to keep her alive long enough to claim her inheritance.

In occupied France during the Franco-Prussian War, a young French laundress shares a coach ride with several of her condescending social superiors. But when a Prussian officer holds the coach over, social standings are leveled and integrity and spirit are put to the test.

After her father dies, Lily moves to the city to live with her strict aunt. During the day Lily works in her aunt's bookstore, and at night she sneaks across the street to model for Richard, a sculptor with whom she falls in love. A patron of Richard's, Baron von Merzbach, develops an interest in Lily that may not be with the best of intentions.

Drummond's girlfriend is kidnapped by his enemies and he along with his friend Nielsen, an inspector from Scotland Yard, follow the trail and try to rescue her from the kidnappers.

Inspector Cassin, a renowned Paris detective, departs to the country for a much-needed break. There he falls in love with the innkeeper’s daughter, Nanette, who is already betrothed to a local farmer. On the evening of their engagement party, Nanette and the farmer both disappear. Cassin takes up the case immediately to discover what happened to them and who is responsible.