Sgt. Rusty Curtis of the U.S. Cavalry is unhappy about the Army's plan to replace horses with tanks so, after a medical discharge, he tries to buy his old military mount Sireson. Unfortunately, the father of wealthy socialite Sally Crandall outbids him with plans to train Sireson for a steeplechase race. Sally and Rusty develop a rivalry because she has a favorite horse of her own, but when her horse is hurt she and Rusty declare a truce and begin a romantic relationship.
Cosmo Jones, a correspondence-school detective from a small town, comes to the big city to offer his services to the police. He happens by where a gangster is killed by an opposing gang. Socialite Phyllis Blake is running around with gang member Tom and the opposing gang plan on kidnapping her. Cosmo is with Sergeant Flanagan when the attempt is made in front of a night club, where a bystander is seriously wounded in the gun-battle. Police Chief Murphy blames Flanagan for the shooting and demotes him. Cosmo, with the aid of a porter, Eustace and Flanagan's fiancée, Susan, tries to find the killer. Phyllis is finally kidnapped and Cosmo decides the act was committed by one of the two gangs. He has her father place an ad in the newspaper that contact has been made with the kidnappers. Each gang thinks the other is pulling a double cross, and one gang wipes out the other.
A private detective, soon to enlist in the army, is drawn into one final case when his police officer father is killed in the line of duty. Soon his prime suspect is murdered as well, and he finds himself framed for the crime. As more witnesses get murdered, he finds himself on the run from both the police and former Prohibition violators who seem to have found a new racket.
Boston pharmacist Tom Craig comes to Sacramento, where he runs afoul of local political boss Britt Dawson, who exacts protection payment from the citizenry. Dawson frames Craig with poisoned medicine, but Craig redeems himself during a Gold Rush epidemic.
Rejected by the Army, Marines, and Navy for being too young, the punks help the war effort by throwing fruit at a shop they believe is owned by a Japanese American. Confronted by him wielding a short sword, the gang decides to come back at night but find him dead.
Henry Courtney, a wealthy importer is found murdered and the famous DeNormand necklace has been stolen. The false testimony of two witnesses, Rand and Hobbs, puts Jim O'Brien in the shadow of the hangman's noose. Martha Courtney, widow of the murdered man and Jim's former sweetheart is convinced he isn't guilty, and promises crooked lawyer Roger Lanning the necklace - which Jim doesn't have - if he can arrange for Jim's escape. Rand and Lanning killed Courtney, but Lanning doesn't know that Rand has the necklace.
Rodeo contestants Johnny King and Corrigan meet, their fathers having been members of the Range Busters. When Johnny is knocked unconscious, time reverts to their father's era and the Range Busters are soon involved in the scheme to get Railroad right-of-way across Mother Slocum's ranch. When she is tricked into signing a release, the Range Busters find their job more difficult as the Sheriff is in with the crooks.
Although young and beautiful, schoolteacher Anne Gladden fears a dull future. She finally decides to take a walk on the wild side, splurging on some fashionable new clothes and setting off to find adventure. Her new confidence inspires her to flirt with complete strangers. When a gangster pays unwanted attention to her, she ditches him and flees in his car, unaware that there's a corpse in the trunk. Determined to recover his stolen vehicle and its incriminating cargo the thug begins a desperate search. The oblivious Anne, comes to the aid of a handsome young man stranded alongside the road. Romance blooms, but after the shocking discovery of a body in the trunk, the duo decide they have to return the car. The bickering lovebirds head back to the city, trailed by both the angry gangster and the cops, who suspect the young couple of murder.
Filmed in the Sierra Nevada mountains near Sonora, California, this Universal serial is Universal's 40th sound-era serial. Eagle Scout Bruce Scott, leader of Martinsville Troop Number One, and his pack sets off in search of lost treasure and finds adventure