A bookkeeper in the employ of a large manufacturing concern lived far beyond his means. He had evil associates and when his debts became very heavy he determined to pay them at the expense of a fellow worker, the cashier for the same concern. One morning as the young cashier reached the office he received a telephone call, purporting to be from the head of the firm, instructing him to leave at once for a western city. He was told to take a certain envelope from the safe and deliver it to the firm's representative there. The young man opened the safe, took the envelope and hurried to his home, where he packed his valise and set out for the station. When he started to pass through the train gates he was seized by detectives and charged with robbing his employer. He was searched and the envelope was found to obtain part of the stolen funds. No one believed his story about the telephone call except the girl to whom he was engaged. The young woman was a detective on the New York police force. She determined to prove the cashier's innocence and secured a position as stenographer with her sweetheart's firm. The bookkeeper aroused her suspicions. She watched him closely, and when he secretly met a shady character noted for his ability as a safe expert, the girl was sure that she was on the right track. She installed a dictagraph in an adjoining office and one evening when the bookkeeper was working late at the office he was confronted by the safe expert, to whom the girl had sent an anonymous letter intimating that the bookkeeper contemplated fleeing from town. In the quarrel which ensued the full details of the plot of which the cashier had been a victim was revealed. The bookkeeper and his accomplice were sent to prison, while the cashier's employer, repentant at having misjudged him, soon made him manager of his business and the girl detective resigned from the department to devote her life to keeping her eye on just one man.