While in London trying to nab several fugitives who stole a million dollars from a U.S. Treasury vault, American federal agent Dennison (Dennis O'Keefe) assists Scotland Yard Insp. McClaren (Philip Friend) in his search for a missing atomic scientist (Paul Hardtmuth). The detective duo discovers that the key to solving both cases may rest with the scientist's daughter (Margaret Sheridan) and her fascinating diamond.
A famed trumpet player is suspected of murdering a blues singer. Using only two minor clues, he narrows the suspects to four people, but only after surviving poison placed on the mouthpiece of his trumpet!
London, 1888: on the night of the third Jack the Ripper killing, soft-spoken Mr. Slade, a research pathologist, takes lodgings with the Harleys, including a gloomy attic room for "experiments." Mrs. Harley finds Slade odd and increasingly suspects the worst; her niece Lily (star of a decidedly Parisian stage revue) finds him interesting and increasingly attractive. Is Lily in danger, or are her mother's suspicions merely a red herring?
Someone is stealing priceless paintings from the great museums of the world and replacing them with nearly flawless forgeries. Leonardo da Vinci's "Madonna and Child" is being shipped to London's Tate Gallery for a special exhibition, and Paul Mitchell is assigned to protect it. Upon the painting's arrival, Paul realizes it has been switched. Eager to collect the museum's $50,000 reward, he teams up with Mary Mason, a Tate employee, to recover the original.
When the available evidence in a murder case points to a young woman as the main suspect, her boyfriend, a police detective, arranges for a struggling songwriter who is playing piano in a bar to be blamed for the crime. The girl, knowing that neither she nor the piano player committed the murder, helps him to escape from the police dragnet and try to find the real killer.
Roy and Gilbert's fishing trip takes a terrifying turn when the hitchhiker they pick up turns out to be a sociopath on the run from the law. He's killed before, and he lets the two know that as soon as they're no longer useful, he'll kill again. The two friends plot an escape, but the hitchhiker's peculiar physical affliction, an eye that never closes even when he sleeps, makes it impossible for them to tell when they can make a break for it.
Upon waking up to the news that the man she’d gone on a date with the previous night has been murdered, a young woman with only a faint memory of the night’s events begins to suspect that she murdered him while attempting to resist his advances.
A vicious loan shark ring has been preying on factory workers. When several workers at a tire factory suffer violence at the hands of the loan sharkers, a union leader and the factory owner try to recruit ex-con Joe Gargan to infiltrate to the gang. At first Joe does not want to get involved, but changes his mind when his brother-in-law dies at the hands of a savage loan shark hood. Joe works his way into the mob, but in order to keep his cover, Joe can't tell anyone what he is up to. This results in him being disowned by his sister and girl friend.
In World War II France, American soldier Michael Blake captures, then loses Nazi-collaborator art thief Paul Rona, who leaves behind a gem studded gauntlet (a stolen religious relic). Years later, financial reverses lead Mike to return in search of the object. In Paris, he must dodge mysterious followers and a corpse that's hard to explain; so he and attractive tour guide Christine decamp on a cross-country pursuit that becomes love on the run...then takes yet another turn.
Mystery novelist Janet Frobisher, lives in an isolated house, having been separated for years from her criminal husband. She has fallen in love with her secretary's fiancé and when her estranged husband unexpectedly returns, Janet poisons him, but just as she's about to dispose of the body, one of her husband's criminal cohorts also shows up.
Frank Johnson, a sole witness to a gangland murder, goes into hiding and is trailed by Police Inspector Ferris, on the theory that Frank is trying to escape from possible retaliation. Frank's wife, Eleanor, suspects he is actually running away from their unsuccessful marriage. Aided by a newspaperman, Danny Leggett, Eleanor sets out to locate her husband. The killer is also looking for him, and keeps close tabs on Eleanor.