A sniper, Oldfield, prepares to open fire on the Wanderer
. Inside, Jim and Artie meet with Rita Leon, who explains that her husband Enrique went to see a man named Thorvald Wolfe to seek work and never returned. Enrique had worked with the agents before and asked Rita to see them if he didn’t return. All Rita knows is that Enrique was made captain head of a post in Mexicale. Jim remembers Wolfe as a munitions expert cashiered out of the Army for taking bribes.
The train whistle goes off, warning the agents of danger. Jim pulls Rita away from the window as the sniper opens fire, shooting an explosive bullet. The agents run out but the sniper gets away. They realize that whoever created the gun is a dangerous man.
Back at the train, the agents reassure Rita that she has nothing to worry about it. All Rita can remember is that Enrique mentioned betrayal and money, but insists that her husband would never betray his country. She directs them to Wolfe’s ranch in Mexico and Jim sends her back home with Artie. He then suggests to Artie that if Wolfe wants a Mexican officer, they give him a colonel instead of a captain. While Artie infiltrates Wolfe’s force, Jim will go in posing as a recent escapee from a Federal prison outbreak. There have been a recent series of freebooter attacks along the border, conducted with the kind of military precision that Wolfe was known for.
Richard Henry, a young government agent, is putting up wanted posters of Jim in his new alias. Jim finds him and shoots at the poster. Richard is eager to help but Jim tells him that his time will come and promises to take him on his next mission if there are pretty girls involved.
Jim arrives at Wolfe’s ranch and tries to ride through the gate, but Wolfe’s men stop him. Their leader, Egan, tries to stop him and Jim kicks him and tackles the others. He is quickly subdued and Egan prepares to shoot him, but Wolfe’s lieutenant Bender comes out and stops him. Bender finds the wanted poster on Jim and figures that he’s worth much more alive.
Jim wakes up in a cell and Wolfe and Bender come to see him. Jim maintains an attitude toward Wolfe and says he was in the Union Army. Wolfe wonders if he can be valuable and Jim suggests that he try him. Bender tries to shoot Jim and the agent knocks him down and takes his gun. Impressed, Wolfe says that he knows all about Jim’s assumed identity and promises him power and glory. He needs daring men and Jim says that he’s a good gun and needs the money. Wolfe gives Jim the freedom of the post on a probationary basis and says he’ll find out about their plans in an hour along with the others.
Once outside, Jim sees men practice-shooting. Crates of munitions from the U.S. Federal Arsenal in San Francisco sit around the central courtyard and other men load them onto wagons. The gunmen have the newest repeating guns. Jim spots Enrique inside of a cell, but before he can investigate, Artie arrives posing as a Mexican colonel, Hernandez Del Valle Santiago y Sandoval. Wolfe greets him and they go inside.
Bender calls Jim and the others into a hall and Wolfe introduces Artie as the Inspector General of Mexico’s northern border. Wolfe plans to conquer Baja California and Artie jumps in. He explains that the Mexican Army will stand by because the Yaqui Indians are in revolt throughout Mexico. Bender takes over, informing them that they have 200 men in Ensenada waiting for them, and they will attack Baja’s northern border. Jim asks what Grant will do and Wolfe says that the Mexicans won’t tolerate American interference in their affairs. He ends the meeting and the men go outside.
Wolf shows Artie one of his new repeating rifles and gives one to Jim for a demonstration. Jim shoots a weathervane, blasting off its head. Artie warns that the Mexicans will move in and Wolfe says that his “turtle” will take care of them. He gestures to one of his men, who opens a door and reveals an armored vehicle with a Gattling gun. Wolfe plans to deploy a dozen of them on the Colorado River and eventually build enough to sweep south into Colorado, conquering everything as he goes. He sends Jim on his way and Bender sends him to a work party. Once Jim goes, the man with Bender, Oldfield, notes that Jim looks familiar.
That night, Oldfield tries to remember where he saw Jim without success. As he and Bender walk by Enrique, Oldfield remembers that Jim was with Enrique’s wife at the train. They go back after Jim, who tries to escape but is quickly surrounded. Bender takes him to Wolfe, who orders Jim locked up.
Once they’re alone, Jim talks to Enrique who explains that the Mexican Army is in disarray as it deals with the internal rebellion. Before they can plan an escape, Bender escorts Artie in. He wants Enrique’s signature on a letter and secretly slips a marble to Jim. Artie then drops his monocle and confirms that Jim and Enrique will be shot the next morning.
Once they’re alone, Jim takes the “marble” of plastic explosive and jams it into the hinges. His vest string is a fuse and Jim uses his boot knife to cut it to length.
Artie meets with Wolfe one last time before he rides off and promises that the men under his command will be ordered out of the way. Once he goes, Wolfe admits that he doesn’t trust Artie but that he’s sure he’ll give the right orders. Once they take over, they’ll dispose of Artie permanently. Wolfe and Bender enjoy a drink and Wolfe admits that he was clumsy and got caught. Now he plans to make his own rules and his own nation, a nation where criminals can come to hide in return for their sworn obedience. Impressed, Bender drinks to their success.
As they wait, Enrique explains that he was assigned to a dead-end job at a border post. Wolfe contacted him and offered the governorship of Baja, but Enrique ultimately turned him down. Jim figures rigging the fuse and shows Enrique Artie’s monocle lenses. He has a $100 bill in his string tie clasp and assures Enrique they’ll light the fuse when Wolfe’s men are distracted.
When he notices that Bender is nervous, Wolfe orders him to form a firing squad and shoot Jim and Enrique earlier. As Bender gathers his men, Artie arrives disguised as a cantina women. He has several barmaids with him, including Rita, and Wolfe’s men quickly gather to enjoy the free drinks they offer. Wolfe comes out and Bender goes over to explain, and Wolfe decides to let his men enjoy themselves.
Jim sets the money on fire and ignites the fuse. The door blasts open and Artie orders Rita and the other women to ride out. He opens fire while Jim and Enrique go to the Turtle. Enrique fires the Gattling gun, decimating Wolfe’s men, while Jim fires the cannon. Wolfe tells Bender to get one of the new rifles. Once he has it, Wolfe fires the explosive bullets, damaging the tank’s motor and wounding Enrique. Jim goes out the roof hatch, kills Egan, and makes his way to the cover of the munitions crates. Wolfe orders his men to cease fire before they hit the munitions and blow up the entire compound. Jim throws dynamite at Wolfe but Bender sacrifices his life to push his superior out of the way. Wolfe runs for it and Jim goes after him while Artie picks up the rifle and fires on the freebooters. Jim easily subdues Wolfe. He brings the freebooter out to where Artie and Enrique have subdued Wolfe's remaining men.
Later, Enrique and Rita visit the agents at the Wanderer
. Jim offers a toast to Rita for ignoring his order and showing up with Artie. Enrique objects to her involvement, insisting that a woman’s place is to obey her husband. Jim can’t help needling Artie about his impersonating a woman, and decides to track down the other two women who helped. Jim is enthused until Rita explains that they’re home with their husbands.