Two outlaws rob a stage, kill the driver and leave the shotgun guard for dead. The guard survives the attack and, with the help of a passerby, manages to make it to Diablo. The man can't defend himself from charges of robbery and murder because the bullet wound has caused complete amnesia. Annie and Lofty set out to prove the man's innocence.
After Annie thwarts a bank robbery attempt, young Smiley Douglas decides it would be a great joke to pretend to rob the bank the very next day without benefit of a weapon. Lofty fails to see the humor in the practical joke, but sets the man free. The outlaw gang who bungled their earlier attempt trick the trickster into helping them rob the bank yet again.
An miner's boastful letters to his grandson living in the East comes back to haunt him when the youngster announces he will be visiting the old man to learn more about his crime-fighting exploits. When the miner fails to prevent a jail break and causes him to lose face with the youngster, he recklessly decides to chase the escaping outlaws.
Della envies Annie's freedom and trick riding skills. When the rodeo comes to town, Della's father refuses to allow her to meet her boyfriend, one of the best competitors. When Della decides to run away, she falls under the sway of an unsavory couple, who agree to return to the ranch to retrieve her clothes. Actually, unintentionally armed with information Della has provided, the crooks plan to rob her father.
When a range war over water rights appears imminent, a masked man wearing a Robin Hood costume supporting the homesteaders knocks down ranchers' fences and stampedes stock. When an impostor dons a similar costume and robs the Diablo bank both sides demand that Lofty bring the criminal to justice.
A telegrapher's desperate message for help forces two murderous thieves to hide their loot in a box of bicycle parts meant for a pair of intrepid cross-country cyclists. The crooks force the cyclists to pedal their ill-gotten loot out of town, but Annie discovers their scheme and lays plans to capture the killers.
Diablo's barber, Paul Denain, is murdered when he refuses to sell his small ranch. His will leaves everything to his daughter who he hadn't seen in years. Annie, acting as his executor, begins a search for the missing heir and soon two beautiful young women arrive claiming to be the long-lost child.
While surveying the route for the first telephone line intended to link remote ranches with the Diablo phone company spot a burning ranch house and arrive at the neighboring homestead in time to drive off the attack. Annie discovers that a crooked businessman has convinced the Indians to burn out the small ranchers so he can buy their land for next to nothing and turn a huge profit reselling the acreage when the Indian troubles suddenly cease.
When a member of Teddy Roosevelt's famed Roughriders returns to Diablo to homestead valuable land he'd been promised for reenlisting, he discovers the property is part of an Indian reservation. A crooked land agent frames the ex-soldier for murdering a brave in hopes of provoking an Indian war, which he will use for his own land-grabbing ends.
A gang of hired killers rides into Diablo. Lofty believes that they're in town to murder a state senator with powerful enemies in the capitol. When Lofty discovers that the gang's leader once rescued him from certain death during their days in the U.S. Cavalry, he is reluctant to take him on and possibly kill him in a shoot-out. As a result, the townspeople force Lofty to resign.
A tenderfoot from Mississippi travels to Diablo to visit his sister and loses his watch in a stagecoach robbery. The headstrong youth is soon telling everyone how to do their jobs - including questioning Lofty's search for the outlaws who robbed him and his sister's experienced ranch foreman about his business methods. The young man really bites off more than he can chew when he discovers the identity of the thieves and tries to bring in the entire outlaw gang single-handed.
During a heated election campaign between honest lawyer Dave Morgan and Carter Holmes, a crooked politician, the contest takes a violent turn when Holmes tries to have his competitor murdered. When his henchmen fail, Holmes hires a notorious gunfighter to take care of the job, but is surprised when the gunman promises to get Holmes to back out of the election without violence.
Sugarfoot Sue Ryan tells so many tall tales that her friends no longer believe anything she says. When her father spots the outlaw gang who stole his horses, but is surrounded by the crooks, Sue rides to the rescue, but Deputy Sheriff Lofty Craig doesn't credit her story.
While riding in the desert, Annie and Tagg meet Tim Lafferty, a strange old Irishman who claims to be searching for treasure with the help of leprechauns who followed him to America from the Auld Country. When a neighbor tries to gain possession of the Biddle family ranch by killing Eliza's brother, Tim proves invaluable to Annie and Lofty by helping them smoke out the killers.
A young man returns to Diablo after attending medical school and his father, the manager of the local express office, spends lavishly to build and equip an office for the young man to begin serving Diablo as its much needed doctor. Unknown to his father, the son fell in with bad company while at school and flunked his medical examinations and, to make matters worse, owes a crooked gambler a large sum of money.
While rummaging through an old trunk, Tagg and his friend Johnny Ward, the son of a murdered lawman, find evidence that they believe proves his uncle is an ex-convict and may be part of the outlaw gang who recently robbed Diablo's bank.
A marshal kills a outlaw who could be a dead ringer for Deputy Sheriff Lofty Craig) if the lawman grew a moustache. Lofty agrees to travel to the Sonoma County Fair and pose as the slain gunman to draw out the rest of the counterfeit ring, but knowing if he's discovered, the gang will kill him as they did a sheriff who got too close to their operation.
John Boone plans to settle in Diablo after years at sea, but learn most of the townspeople hate him because his father caused the death of one of the town's most beloved citizens when the two old men died searching the desert for pirate's treasure. Boone is convinced that a chest full of gold coins really has been buried in the wasteland and convinces Annie, Lofty and Tagg to join the hunt.
It's the social event of the season when Sand Creek's newspaper editor marries a beautiful brunette, but joy turns to sorrow when an outlaw gang takes advantage of the ceremony to rob the bank and kill the sheriff, who was serving as the groom's best man. Lofty captures a drifter and hold him while he investigates the crime, but the grief-stricken newspaperman fans the town's hatred of the man with his biased reporting.
Lofty and Annie become concerned when homesteaders are forced to sell their spreads cheaply because of rustlers, poisoned waterholes and cut fences. Annie tries to find out if the land-grab has anything to do with an earthquake that rocked to area immediately before the crime wave began.
Tagg Oakley is tricked into driving a wagon full of gunpowder to Fort Yuma not realizing that Geronimo and his Apache braves have been tipped to the time and route of the delivery. Lofty attempts to rescue the boy before he comes to harm, while Annie tries to arrest the renegade who sent the boy into harm's way.
A old female peddler is injured when her team of horses bolts. While she recuperates under Lofty's care, Annie writes to her estranged son in Texas and asks him to visit his ailing parent. Little does Annie know that young man has joined an outlaw gang and brought them to Diablo to resume their criminal activities.
A young man is mistaken for a notorious outlaw and has a hard time convincing Diablo's townspeople that he didn't commit a stagecoach robbery. Though Annie Oakley and Susan Meriwhether believe him, their confidence is shaken when he is present went the town's bank is robbed by outlaws who appear to recognize him.
Annie and Lofty try to close the local gambling hall without success. It's owner, the son of a legendary lawman, is convinced that making money is more important than being respected. The young man changes his mind when outlaws pistol whip his father. He agrees to take them across the border to safety, but instead leads them on a wild goose chase.
When their handicrafts meant to trade for goods at the local trading post are stolen by white men, the Navajo tribe decides to seek vengeance by going on the warpath. Since whites are forbidden to enter the reservation, even to seek peace, Annie must dress as an Indian maiden to prevent bloodshed.
When Annie captures the outlaw who stole Gentleman Jim Corbett's championship belt and returned it to its rightful owner, the ex-world's heavyweight champion volunteers to fight in an exhibition boxing match to raise money for Diablo's new school. Lofty reluctantly agrees to face Corbett when no one else will, but an outlaw gang breaks one of their members out of jail during the bout.
A elderly sharpshooter, Snowy Kringle, arrives in town for show where he will demonstrate his skill with a flintlock rifle and cap-and-ball pistol. The man who is charged with delivering the Army payroll warns the Deputy Sheriff that the old sharpshooter is really a crook and is probably after the payroll. When the express office is robbed, all the evidence points to the old man, but Annie suspects he's been framed for the crime.
Annie, Lofty and Tagg try to help a young Indian when he inherits a stagecoach line with a valuable mail contract after his white patron, the owner of company is bushwhacked and murdered. A rival businessman who craves the contract tries to frame the young brave so he can take over the valuable concession.
After years of fruitless prospecting, old Scissorbill Childers finally strikes it rich and decides to use his new-found wealth to open a bank to grubstake other prospectors who are searching for gold and silver. New found wealth always attracts criminals so Lofty has his hands full trying to thwart claim-jumpers and swindlers. To make matters worse, the government assayer determines that Childers' gold ore comes from the same claim as that of a murdered prospector.
Annie, Tagg and Lofty try to help a history buff who believes he has found a map that could lead to gold hidden by the Spanish explorer Coronado over in the early 1500s. The man's search for the treasure is hindered by a gang of outlaws who want the loot for themselves.
Annie and Lofty investigate when two outlaws hold-up the messenger carrying the Cattlemen's Association receipts to the bank. They loose the trail near the shack of a strange old junk collector who claims to have no knowledge of the robbery or the criminals. Annie doesn't buy the man's story and sneaks into the man's home to search for clues to where the money has been stashed.
An ex-convict recently released from prison is killed by outlaws before he can recover the gold he stole ten years earlier. The crooks believe he may have confided the location of the hidden loot to his son. When the youngster insists on visiting a ghost town while en route to his aunt's home in Colorado, it appears that the boy may know something after all.
A retired army officer who has been recalled to active duty in Washington decides to sell his valuable ranch for less than market value just to be rid of the property. He places advertisements in every major newspaper west of the Mississippi seeking buyers. His advertisement not only attracts men interested in real estate, but outlaws who are interested in the large sums of cash the buyers are carrying.
A Dutch gunsmith, the inventor of an new rifle with superior range, plans to give the weapon to the United States Army in gratitude for being allowed to immigrate. A crooked businessman decides to take advantage of the man's patriotism and sends an impostor posing as an officer to take possession of the gun before the real colonel can arrive in Diablo.