Slip and Sach are in the sidewalk star-gazing business when they see a murder committed in a room at the El Royale Hotel.
After Slip is drafted into the Marines, the rest of the gang volunteers so they can be with him. Sach discovers that the colonel knew his father and he is promoted. During a drill that he is putting the rest of the gang through, they find a soldier left for dead on the side of the road. Slip discovers a playing card next to the marine and traces it to Jolly Joe Johnson's gambling house. They suspect that the gambling house is cheating and set out to uncover the proof.
An electric shock enables Sach to predict numbers, so the Bowery Boys are off to Las Vegas to win enough money at the roulette wheels to let their landlady buy an apartment building. Witnessing his winning streak, some gangsters decide to move in and find out his "system" for beating the odds.
In order to be able to get the names of winning horses at the track, Sach agrees to sell his soul to the devil.
The Bowery Boys--Slip, Sach, Bobby, Whitey & Chuck--start their own exterminating service, and get a job which takes them to a spooky old abandoned mansion in the middle of the night. Meeting up with pal Gabe and his new French bride, the boys are tormented by mad scientists who try to convince them the place is haunted and then kidnap Sach in order to place his brain inside a gorilla.
Slip (Leo Gorcey), Sach (Huntz Hall), Bobby (Bobby Jordan), Whitey (William Benedict) and Chuck (David Gorcey) unsuccessfully try to sell a dilapidated car to a street cleaner for a fabulous amount, so they can get enough money to save Louie's (Bernard Gorcey) Malt Shop. Sidewalk photographer Cathy Smith (Teala Loring) snaps a pictures of three bank robbers as they are fleeing a robbery but when the Bowery Boys and Cathy realize that Sach is also in the photograph, they break into the photo lab to destroy the negative, which might make the police think Sach was involved in the robbery.
The Bowery Boys head west to clear Louie of an old murder charge that he had killed his gold-mine partner. Sach has the map to the gold mine painted on his back, and Blackjack McCoy has him kidnapped by Indian Joe. Gabe poses as a dangerous gunman, the Klondike Kid, while Slip is in charge of all the remaining loose ends.
Slip, Sach and the rest of the Bowery Boys enter a haunted house, where they engage in slapstick with a gorilla, a robot and a vampire
A ghost helps the Bowery Boys capture a gang of crooks led by a mad doctor.
The Bowery Boys are enrolled in a fancy college by a pair of rich snobs who think they can turn the Boys into classy guys. Sach becomes a football star, and is kidnapped by gangsters to keep him out of the big game.
Slip has entered the Boys' rattletrap car in a souped-up jalopy race, but has no chance of winning until Satch, with the aid of a scientist acquaintance, comes up with a chemical concoction that acts as a super-fuel; but a rival entrant in the race learns of this and tries to get the formula for himself.
The boys buy a uranium mine out west, but when they get there they find that it's pretty much worthless. However, the local badmen are distrustful of these new strangers, and when they mistakenly get the impression that the mine is loaded with uranium, they hatch a scheme to get rid of the boys and take over the mine.
Slip gets fired from his job at a construction company for decking his boss. His sister, who got him a job at the company, is angry with him. Slip manages to get a job with the District Attorney serving warrants, as does Sach. Through his job, Slip finds out that all is not quite kosher at his old construction company, and that his sister may be in danger.
When Sach eats too much sugar, he goes into a trance whereby he's able to predict the future. Slip tries to make some money off of Sach by using him as a fortune teller in a carnival, until a mad scientist kidnaps Sach to use him in an intelligence-switching experiment with a monster.
The Bowery Boys tangle with Scotland Yard, diamond smugglers and a gem-toting canine during an ocean cruise.
While Louie is on vacation, the boys turn The Sweet Shop into an escort service, and soon find a group of beautiful girls as their first clients.
When a cold medicine causes Sach to be able to smell diamonds, he and the rest of the Bowery Boys are induced by a diamond dealer to accompany him to Darkest Africa in search of a legendary cache of them.
The Bowery Boys join the Navy to catch some crooks who are posing as sailors.
After being punched in the nose, Sach finds out that he has the ability to read minds. Slip and the gang start up a detective agency try to cash in on Sach's new powers.
Sach receives news that he is the heir to the Terwilliger Debussy Jones fortune. Accompanied by his pal Slip, he arrives at the Jones mansion to review the legal papers needed for him to claim his new fortune. However, Sach and Slip discover that the rightful heir, the young Terwilliger III, is being cheated out of his inheritance by the miscreant duo of Stuyvesant Jones and Clarissa. Sach and Slip, with the help of their fellow Bowery Boys, save the day and restore the heir’s inheritance.