The Wanderer is passing through Kansas when it stops at Kirby Gap for water. Jim and Artie decide to go into town and discover that Amos Rawlins, the local rancher, is holding a feast for the entire town to celebrate the shipment of cattle for the season. Rawlins addresses the crowd and calls up his wife, Eugenia. Jim and Artie join the food line and watch as banker Roger Creed approaches Rawlins and complains that he's spoiling the workers. Rawlins jovially invites Creed to join the feast and the banker drops his cane. A shot rings out and hits Rawlins in the head, killing him. The killer runs off, brushing past a local woman, Abigail Moss. She manages to tear off the pocket of his jacket but he keeps on going. Jim runs in pursuit and follows the killer up to a second-story hotel room. The agent bursts in and finds the killer sitting calmly on his bed, holding the gun. His jacket is missing a pocket, but the killer doesn't put up a fight. Jim takes his gun and puts him under arrest.
A jury is quickly put together and a trial held. Prosecutor Franklin Poore informs the jury that the killer, Lucius Brand, intended to kill Creed, who had foreclosed on his farm when a drought hit. Abigail confirms that Lucius was the man she saw and Jim testifies to what he saw. Lucius testifies on his own behalf and claims that he had just woke up when Jim burst in. He sent his pregnant wife to live with family and was staying at the hotel, and had too much to drink the night before so he was asleep. Lucius can't account for the torn pocket or the gun, even though it belongs to him. The jury finds him guilty and Judge Blake orders him to hang in two days. When Lucius makes a futile attempt to escape, Jim stops him but then stops Sheriff Jonas Bolt from shooting the defendant trying to escape. Lucius' wife, who has returned to Kirby Gap, angrily rounds on Jim for getting her husband convicted and insists that he's innocent.
Outside, Jim admits to his partner that the fact it was such an easy case to settle bothers him. Artie would rather move on, but admits that he's intrigued at some of the holes in the case. They go to see Lucius in jail and offer their help, asking him more about what happened. Lucius, who has accepted his fate, tells them that he was drinking with a couple of Rawlins' ranch hands the night before. He had too much, passed out, and woke up in his bed at the hotel. Lucius saw his gun on the floor and picked it up, and that was when Jim burst in. When Jim wonders why he woke up at the precise instance, Lucius says that he had a nightmare of a train bearing down on him.
The agents go to Lucius' hotel room and search the place. Jim is surprised when Artie vanishes and then talks to him out of nowhere. Artie tells him to sit in a chair and move an arm panel. When Jim does so, he's shot up through the ceiling into the attic. Artie has found a device that makes the sound of a train engine, and they figure the killer ran into the hotel room and used the chair to escape, while his partner woke Lucius up with the device. However, the attic suddenly bursts into flame as someone sets a fire to cover his tracks. The agents use a spike and line to drop out of the window to safety as the building goes up in flames.
Jim goes to see Poore, Judge Blake, and Sheriff Bolt. He asks for a delay but admits that all of the evidence they had was destroyed in the fire. Blake initially agrees but Bolt warns that the townspeople could riot if they order a stay without a riot. The judge quickly reverses himself and tells Jim that they'll need more proof.
Back at the train, Artie shows his partner daguerreotypes taken at the celebration. The killer avoided having his face in any of them, but Artie finds one which shows a street vendor releasing a balloon. The agents figure that was the signal for the killer to fire. Artie blows up the image of the vendor and Jim goes to the novelty company while Artie goes to see Abigail.
Artie disguises himself as a reverend and visits Abigail at Mrs. Peacock's Boarding House. Mrs. Peacock refuses to let him in until he compliments her, but insists on serving him her lousy cooking first. Artie finally gets her to tell him that Abigail left that morning to get some jewels left to her by her dead uncle. Mrs. Peacock finally says that Abigail is taking the noon stage, and Artie runs out, yelling that he doesn't want to sample her cooking.
Jim breaks into the novelty store and starts searching. He finds two piece of clay pipe that form a small derringer-like gun-shape. Three thugs attack Jim and he takes care of them, and hears someone in the back office. Pocketing the pipes, he runs in but the doors close, sealing him in. Poison gas pours into the room and Jim uses a windup wheeled toy with some of his explosive to safely blast the door open so he can make his escape.
Artie gets ahead of Abigail's stage disguised as Henrick a jewelry salesman. When the driver takes him on, Artie initially plays suspicious to attract Abigail's attention. He soon warms to her and they discuss jewelry, and Abigail shows him her new ring. Artie lies and tells her that it's costume jewelry, making her think the person who paid her off double-crossed her. The stagecoach arrives in Paradise Flats and Abigail prepares to go back to Kirby Gap. Meanwhile, Artie attaches a message to the homing pigeon he has in his fake jewelry case and sends it to Jim.
Jim is at the Wanderer examining the two pieces of clay when he gets Artie's message. He goes to the stagecoach office and watches her arrive and then go immediately to Poore's office. As she argues with the attorney, Jim catches just a glimpse through the window of another man's hand. As Poore slaps Abigail, the man closes the drapes. Jim enters the office but discovers that no one is inside. Poore comes in and Jim accuse him of paying Abigail to perjure herself in court. However, when the agent tries to take Poore to Judge Blake, Poore's thugs knock him out from behind and take him into a secret room.
When Artie arrives at the Wanderer, Mrs. Brand emerges from the back and prepares to kill him and then Jim once she finds him. Undeterred, Artie cheerfully informs her that he can clear her husband's name. He sets up the daguerreotype projector and shows her two images from the celebration, and demonstrates that based on the angle of the shot that Lucius supposedly made, a man atop a horse was in the way. Once he's assured Mrs. Brand that her husband is clear in the clear, Artie goes to show Poore the evidence.
In Poore's secret office, his men suspend a lamp from the ceiling by a string and tie Jim up beneath it. Poore then spreads lantern oil around and puts a burning candle beneath the string. He then leaves as Jim struggles to slip his bonds.
When Artie arrives, Poore and Creed meet with him. Knowing that Artie is onto their plan, Poore captures him and takes him into the secret room with Jim. After his men tie up Artie, they all leave, and Jim gets free using his hidden collar knife. He cuts himself free just in time to catch the lamp as the string breaks. As he frees Artie and they head for the door, Jim notices an umbrella stand. An umbrella inside of it has a handle that matches the two pieces that Jim found at the novelty shop. The agents realize that the umbrella belongs to Eugenia Rawlins, and that she shot her husband while the fake shooter provided a distraction. Eugenia and her men come in and explains that she hated Kirby Gap and she hated her husband for bringing her there, when she was an elegant woman back East. Jim and Artie knock out the thugs and capture Eugenia, and take her to clear Lucius' name.
Later, Jim and Artie meet Lucius and his wife at the Wanderer to celebrate his freedom. The agents explain that Eugenia's family went bankrupt and she had to marry Rawlins, and approached Creed to help her dispose of her husband. Poore helped them in return for half of Rawlins' money and the banker's support when he ran for office. Jim changes the daguerreotype on the projector and they find that the next one shows a beautiful woman. Artie is taken with her but is disappointed when Jim explains that it's Abigail, a conwoman using one of several disguises. However, Jim assures her partner that she has visiting hours at the state prison on the first Monday of every month.