Hopeless but eager would-be private detective Cedric Gull has just obtained a diploma from a backstreet "School of Detection" and is keen to put his new qualification to good use. Fortuitously, he happens to stumble across a crime scene at the office of a diamond merchant, who has just been robbed and assaulted and is being tended by his secretary Sylvia. The police arrive on the scene, but despite Cedric's proud boasts about his sleuthing qualifications, they decline his kind offers of help.
As described in a film magazine, Tommy Frazer is part of a gang of crooks led by Tony the Wop and Kelley's Cafe is their hangout. One night gang member Skinny is killed by a member of a rival gang, and police officers, hearing the shooting, come to the flat. The police find Skinny sitting at a table, apparently playing cards, so they leave, not noticing that a gang member was behind Spider and holding the cards.
Captain David Guest, a sailor with a fearsome reputation, befriends young Peter Farrell, from a wealthy family, who has got involved with crook Flash Lawson. Believing he has killed a man, Farrell is holed up in a riverside pub, waiting for Lawson to smuggle him out of the country. Guest is kidnapped by Lawson, but escapes and has him arrested, and clears Farrell of the murder charge by revealing the alleged victim to be alive and well.
Jewel thieves Rand, Tom Gordon, Rocco, Boris, and Countess Sonya meet at the California Hotel to await Lillian Vanderhoven, a former burlesque dancer who is now a wealthy dowager and has acquired an expensive diamond known as the "Kimberly King Diamond". Alongside the group is Valerie, Gordon's niece. Valerie meets Rand and becomes convinced he and Gordon are friends on vacation.
Ex-army Captain James Kent is out of work, and gets involved with a gang of thieves, but decides to go straight when he falls in love with lady detective Joan Collinson.
Lady Caroline invites engineer and part-time crime writer Peter Kerrigan to Marsh Manor to solve a murder. Is the mysterious death of a librarian connected with the Claydon treasure, reputedly hidden on the estate a century earlier?
A young postman becomes involved in the theft of rare stamps featuring inverted images of the Statue of Liberty. Along the way he encounters attractive criminal Clara Kelso, double-crossing gang members, and Post Office Inspectors, before finally capturing the crooks.
In the late 1920s, "Lucky" John Hart has a reputation as a stock market speculator. He does an interview with reported Phil "Stu" Stuart, which predicts the Wall Street Crash. Hart sells his investments just before the Crash.
Mather, a US Army officer, is on the run after committing murder. He invades the home of the widowed Peggy and orders her son Tommy at gunpoint to guide him through the backwaters of the English countryside to safety, but he fails to reckon with Joe, a U.S. Army captain, who is in love with Tommy's mother.
