Insurance investigator Sam Donovan is looking into the apparent suicide of a man in a small Midwestern town. All clues leads him into suspecting murder. Unfortunately, no one wants to assist him with the case, including Sheriff Larry Best.
Hank Wilson is a driver for a truck for a big transportation company which is in financial straits. He is in love with Doris Lacy, a waitress at the truck-stop where the company has its truck fleet serviced. Frequent accidents near the place leads the company to hire a private detective to investigate, and when the detective is murdered Hank is arrested as a suspect. The insurance company that covers the fleet has him released and he is sent back to work with instructions to investigate the accidents on his own. The trail leads to the uncle of Doris, and one of the part-owners of the company.
Captain Hugh "Bulldog" Drummond is called in to solve the murder of a man from whom two lead soldiers were stolen. Drummond learns that the two soldiers were part of a set of thirteen which formed the key to a hidden vault of treasure. Following some clever sleuthing and set-up on Drummond's part, the guilty man is trapped in the vault,which is hidden behind the fireplace.
In early 20th century Czechoslovakia, a gravely ill chemist recalls his discovery of a powerful explosive and how it landed in the hands of anarchists.
Michael Lanyard is suspected of stealing two fabulous diamonds from a vault in Scotland Yard, where they were being held for safekeeping, but the Yard can't prove he did it. Later, Lanyard is summoned by a member of the nobility to help the latter raise money to pay a blackmailer. Lanyard later finds evidence to reveal the diamonds as having been stolen by a famous stage star.
A gang of criminals, which includes a piano player and an imposing former convict known as 'Gruesome', has found out about a scientist's secret formula for a gas that temporarily paralyzes anyone who breathes it. When Gruesome accidentally inhales some of the gas and passes out, the police think he is dead and take him to the morgue, where he later revives and escapes. This puzzling incident attracts the interest of Dick Tracy, and when the criminals later use the gas to rob a bank, Tracy realizes that he must devote his entire attention to stopping them.
Sandra Carpenter is a London-based dancer who is distraught to learn that her friend has disappeared. Soon after the disappearance, she's approached by Harley Temple, a police investigator who believes her friend has been murdered by a serial killer who uses personal ads to find his victims. Temple hatches a plan to catch the killer using Sandra as bait, and Sandra agrees to help.
Scotland Yard Inspector Geoffrey James comes to the United States looking for a band of international gem-thieves who have smuggled a rich load of jewels from England to America via a trans-ocean airline. Mary Hogan, an airline hostess, aids him in his quest.
Hoppy, California and Lucky take refuge from a storm inside a supposedly abandoned church outside a ghost town, only to meet a young woman and her mother there, then find themselves surrounded by a gang of "workmen" intent on tearing down the church if they have to kill the five to do it.
Sach just lost his job as an assistant to a private detective, but he wasn't paid. Slip goes with him down to the detective's office to demand payment, but finds the office empty. A woman enters the office and mistakes Slip for the detective and convinces him to take on a case to find her sister after offering a $50 retainer.
The dream is unusually vivid: Bank employee Vince Grayson finds himself murdering a man in a sinister octagonal-shaped room lined with mirrors while a mysterious woman breaks into a safe. It is so vivid that Vince suspects it may have really happened. To get the dream off his mind, he goes on a picnic with some relatives. When a thunderstorm forces his party into a nearby mansion, Vince discovers that the bizarre room does exist, and it means nothing but trouble.
Ronnie Jackson is a lowly baby photographer who secretly fantasizes about being a private detective. When a lovely baroness actually mistakes him for one and asks him to help locate her missing husband, Baron Montay, Ronnie finds himself agreeing. Several days later he is on death row whiling away the hours until his execution by recounting to a group of reporters the bizarre tale of how he ended up there.