A private detective named William 'Bill' Reardon is unexpectedly awakened one morning by his wife, Sally, who appears dizzy and confused, unable to recall the purpose of the string tied around her finger. This seemingly small detail hints at her forgetfulness, which becomes more notable as the story unfolds. During breakfast, the Reardons discuss the financial struggles facing their private detective agency, emphasizing the difficult position they are in both professionally and financially.
Suddenly, Bill receives a call from his only client, Mr. Stone, who is upset because Bill has missed an important meeting regarding recent jewelry store robberies—a matter of rising concern for everyone involved. Sally was supposed to relay this information, but her confusion prevents her from doing so. Realizing the urgency, Bill hurries to meet with Mr. Stone, along with Mr. Davis, the store’s manager and former owner, and Mrs. Nacelle, the wife of the wealthy store owner. During this meeting, Bill confidently informs them that he has a strong suspect: Charles Crenshaw, a clerk at the jewelry store.
However, the plot thickens when Charles Crenshaw makes an unexpected visit to the detective agency, seeking help. He wants to find out why he's being followed, as he recently noticed a mysterious man searching his apartment. Sally, keen to support her husband's failing business, deceptively pretends to be a detective herself and agrees to take on Crenshaw’s case. But the twist reveals itself when it turns out that the man following Crenshaw is actually Bill Reardon, in disguise as part of the investigation.
Later that day, Bill has a lunch meeting with the alluring Mrs. Nacelle, who reveals that her husband took over the store from Mr. Davis because he owed her family money. She suggests that Davis might resent losing the store and could possibly be involved in the thefts. Unaware to Bill, Sally happens to overhear their conversation and, convinced of Crenshaw’s innocence, quickly leaves to warn him by calling the young clerk at the jewelry store. Her attempt to intervene is successful, and soon after, Crenshaw is apprehended by Bill and his agents.
The evening brings the Reardons to a luxurious nightclub where they join the Nacelle couple for dinner. During the night, Mr. Davis is observed leaving the nightclub and picks up a note left at the hat check stand, which was intended for Tony Croy, a notorious mob boss. Croy arrives shortly after and inquires about the note, but the hat check girl states it was picked up by another man claiming to be Croy. Davis then secretly follows Croy in a cab, where they observe Davis reading the note—revealing a location within a file cabinet at the jewelry store that holds some unnamed object. Davis heads to the store to investigate, but tragically, he is shot by an unseen assailant before he can reveal what he discovered.
Meanwhile, Sally concocts a rash plan to clear Crenshaw's name: she intends to steal jewelry from the store while Crenshaw is still in jail, hoping to prove his innocence. Using keys she lifts from Mrs. Nacelle’s purse, Sally sneaks into the store and steals several items. Bill, meanwhile, finds Davis’s note and recognizes its significance to the ongoing case.
Their investigation uncovers a shocking truth: Croy and Mrs. Nacelle had been secretly married but never divorced. Croy has been blackmailing her, forcing her to steal from her husband's store as part of his scheme. When Croy visits Mrs. Nacelle’s mansion to collect the illicitly stolen jewelry, she outsmarts him by tricking him into opening a safe rigged to fire a concealed gun, revealing her cleverness and determination to end his blackmail.
In a dramatic climax, Bill demonstrates that Davis was actually killed by a trick gun concealed inside a file drawer, which fired when opened—similar to the device used at Mrs. Nacelle’s home. The rigged filing cabinet was intended to kill Croy, but Mrs. Nacelle's plan backfired, leading to her confrontation with the police. The story culminates in a final trap set by Bill and Sally, exposing Mrs. Nacelle as the murderer and criminal mastermind behind the thefts and blackmail scheme.
Through ingenuity and persistence, Bill and Sally successfully solve the case, bringing justice to those involved in the criminal activities, and proving that even in the face of deception and danger, good detective work can prevail.
