Wealthy murder mystery writer Paula Bradford (Jean Arthur) returns from her worldwide travels to see her former husband, surgeon Dr. Lawrence "Brad" Bradford (William Powell). He had divorced her because she was always involving him in real-life murder cases, but she wants him back. When a jockey riding the favorite dies while leading a race, she is convinced it was murder. She and Mike North (Frank M. Thomas), the horse's trainer, persuade the reluctant doctor to investigate. Brad is puzzled when he finds traces of gelatin on the corpse.
Un groupe de voleurs, composé d'une femme Vivian Palmer et de deux hommes Ed et Harry pille des bijouteries à Paris. Ross McBride, un agent du gouvernement américain tombe sur Vivian qui essayait de fuir le pays avec le butin et ses acolytes. Les deux protagonistes s'éprennent l'un de l'autre. Ross McBride apprend la vérité sur Vivian Palmer. Il l'arrête
Dans le somptueux manoir de la famille Federie, l'infirmière Sarah Keate prête main-forte au lieutenant Lance O'Leary afin de démasquer le meurtrier du patient dont elle avait la charge.
Arthur Ferguson Jones (Edward G. Robinson) and Wilhelmina "Bill" Clark (Jean Arthur) work at the same advertising firm. Jones turns out to look exactly like the notorious bank robber "Killer" Mannion (also Robinson) and is apprehended by the police.
Nick Charles (Powell), a retired detective, and his wife Nora (Loy) are attempting to settle down. They are based in San Francisco but decide to spend the Christmas holidays in New York. There he is pressed back into service by a young woman whose father, an old friend of Nick's, has disappeared after a murder. The friend, Clyde Wynant (Ellis) (the title character "thin man"), has mysteriously vanished. When his former secretary and love interest, Julia Wolf, is found dead, evidence points to Wynant as the prime suspect, but his daughter Dorothy (O'Sullivan) refuses to believe that her father is guilty. She convinces Nick to take the case, much to the amusement of his socialite wife. The detective begins to uncover clues and eventually solves the mystery of the disappearance through a series of investigative steps.
Gold-digging chorus girl Mary (Carole Lombard) marries the head of a bootlegging syndicate, gangster "Shoots" Magiz (Nat Pendleton), but the illegal liquor business goes down the drain when Prohibition is repealed, and Shoots is knocked off by rival Daniel Dingle (Sam Hardy). Mary, looking for a new sugar-daddy, hooks up with Dingle, and when Dingle is removed from the scene by Mickey "The Greek" Mikapopoulis (Leo Carrillo), transfers her attention to him in return for a "trust fund". All the time, fast-talking straight-shooter Jimmy "Office Boy" Burnham (Chester Morris), Shoots' former bodyguard and errand boy, has looked after Mary, passing her advice and snappy remarks whenever they're needed. In the end, Mary and Office Boy end up together, but only after "Merry Widow Mary" gives away all the dirty money she was given.
Amid vignettes involving a philandering husband who fakes amnesia, a child prodigy who yearns to live a normal life, an aging bachelor whose housekeeper has disappeared, and an old lady whose daughter has run away, the primary plot line focuses on brash detective Butch Saunders, who is assigned to find missing Chicago banker Therme Roberts. Butch finds himself attracted to the man's wife Norma, despite the fact they're both married, so when his superior, Captain Webb, tells him she really is Norma Phillips and the man she claims is missing is not her husband but the person she has been accused of murdering, he doesn't believe her. Norma fakes her suicide by drowning and disappears, but can't resist returning when Butch stages her funeral in the hope she'll surface. Not only she but the missing Roberts, as well, turn up at the services. Norma tells Butch she once was Roberts' secretary, and he killed his mentally disturbed twin brother and assumed his identity in order to avoid embezzlement charges. Roberts denies her accusations, but Webb tricks him into admitting his guilt. Norma is cleared and, when Butch learns his wife Belle never divorced her first husband, the two are free to wed.
Gwen Parker (Mae Clarke) meets her former boyfriend Philip Seymour (Donald Cook) at the local aquarium and asks him for some money so she can leave her husband, stockbroker Gerald Parker. However, Mr. Parker receives an anonymous telephone call tipping him off to the rendezvous. When he confronts the pair, Seymour knocks him out with a punch. As there are no witnesses to the altercation, he hides the unconscious man in the room behind an exhibit.
Marie Morgan (Ginger Rogers) has been lured to an old abandoned house by a false note from a friend, and is in jeopardy although she doesn't yet realize it. As she sits at the table inside, she thinks back to the banquet held there 13 years earlier, when she was a little girl. Only 12 of 13 guests had attended, and the manor's owner, the Morgan family patriarch, who was then dying, has since passed on. The chance to claim the bulk of the estate fortune has resulted in an ongoing campaign of murder by someone targeting the original 12 guests, whose dead bodies are being left at the table in the same seats they had occupied originally.
Un jeune homme, Charles, opérateur dans un cinéma de quartier, est soupçonné d'avoir participé à un vol de bijoux. Sa fiancée, Lucette, voudrait le sauver mais il faudrait, pour cela, dénoncer son frère Olivier qui est le chef de la bande de voleurs. Lucette va voir la victime, le bijoutier Van-Hoolst qui consent à retirer sa plainte contre restitution des bijoux. Les voleurs ne respectent pas le marché mais, finalement, l'opérateur est innocenté et devient propriétaire du cinéma.