Bessie Blake, detective, saves the life of Tom Sterling, the son of a millionaire broker. Thrown in each other's society, Tom's admiration ripens into love, but Bessie is ambitious to rise in her profession, and anticipating Tom's proposal, leaves for the city without divulging her occupation or giving her address. Tom's sister, Marion, on her wedding day receives from a wealthy uncle, an antique box, containing a single unset ruby. Felix La Trobe, a friend of Tom, suggests that the stone be carefully watched during the wedding reception, and Bessie Blake is assigned to the case. Bessie poses as a maid in the Sterling home and renews her acquaintance with Tom. Felix La Trobe constitutes himself the guardian of the ruby, and convinces himself that the precious stone is safe. The next morning the ruby has disappeared. Felix investigates, and accuses Bessie. She, however, astounds them all by disclosing the fact that Marion had unconsciously pressed a hidden spring, which caused the ruby to drop into a secret compartment.
—Moving Picture World synopsis