A Mexican bandit, La Carniceria ("The Butcher") leads his commander's men along the river. They have a prisoner in tow and hear the whistle of the Enterprise up ahead as it approaches the town of Taylorsville.
On the Enterprise, Grey and passenger Lucy Bridges are chatting when Bill comes down and points out the bandits, gathered on shore. La Carniceria leads the prisoner to the water's edge and executes him for helping put their leader in jail. The bandits ride off and Grey sends a boat ashore so the crew can bring the man's body back.
In Taylorsville, Lt. Dave Winslow visits with Sheriff Dave Matson. The lieutenant wonders when the Enterprise will arrive since he's booked for passage to Chicota Landing. Winslow will pick up 2,000 pounds of government gunpowder, deliver the explosives to Ft. Jackson, and return to Taylorsville. Matson suggests that he takes it easy, and notices Winslow eying a local woman, Margaret. The sheriff jokingly advises Winslow to stay away from her since she's engaged to his deputy, Sam Bates.
The Enterprise arrives and Winslow runs to the dock. The townspeople gather when the crew bring the dead man ashore and Matson confirms that the man is Sam Bates. Margaret collapses, sobbing, and Grey tells Matson what happened. Furious, Matson goes to the jail with Grey and Bill in tow. A Mexican wearing a tattered generale's uniform is in a cell and Matson storms in and attacks him. Grey holds Matson back until he gets hold of his temper and the prisoner introduces himself as Generale Juan Cortilla. When Grey explains that he witnessed the bandits kill Bates, Cortilla takes Grey's name in case he ever wants to take passage on the river and goes back to playing his guitar.
As Matson takes Grey and Bill's statement while Winslow looks on, the townspeople come storming up to the jail, intent on lynching Cortilla. Matson refuses to let them in and warns them that he has three men with guns. When Grey objects, Matson deputizes him and Bill. As the mob start breaking down the door, the sheriff tells his new deputies to go outside and stall the mob while he and Winslow take Cortilla out the back. They fire a shot through the door to force the mob back and then Grey and Bill go outside while Matson and Winslow drag Cortilla out of his cell and through the back door.
When the mob gets out the torches, Grey and Bill run. The townspeople set the jail on fire while the partners head back to the Enterprise. Lucy greets them and Grey takes her to the grand salon to get some coffee. He's surprised to find Matson, Winslow, and Cortilla there. Matson explains that the Enterprise was the safest place he could think of. The sheriff then tells Grey that he'll keep Cortilla for the next seven days while the townspeople cool off. By the time the Enterprise travels to Chicota and then returns to Taylorsville, Matson figures the people will have regained their senses. Grey objects, pointing out that they're not a prison ship, but Matson appeals to his conscience, pointing out that the townspeople will kill Cortilla otherwise. The captain reluctantly gives in while Cortilla eyes Lucy appreciatively and asks for an introduction.
The Enterprise leaves Taylorsville and Grey has Cortilla manacles to a support post in a cabin. When he checks on the prisoner, Cortilla says that he's been in chains before and that his uniform is legitimate... to a point. He tells Grey that he worked his way up through the ranks and earned his medals in battle. However, he could never become an officer because his father was a peon. Grey sympathizes with him for deserting, and Cortilla assumes that he'll release him. However, the captain tells him that he has no sympathy for a man who looted and pillaged and lead others to do the same. Furious, Cortilla spits at him, vowing to have him shot, and Grey casually shoves him aside and leaves.
On deck, Winslow is chatting with Lucy, whose father is a colonel in the army. The clearly-smitten lieutenant jokingly proposes to her, saying it's standard Army tactics to advance on a desired goal. Grey comes along and jokes about Lucy marrying him, and tells them that they'll arrive at Chicota Landing the next day. From there it's another day to Ft. Jackson and then three days back to Taylorsville. As they talk, La Carniceria and the bandits ride along the shore, whooping and shooting into the air. As Bill comes down to investigate the noise, Grey tells his partner that the bandit must know that Cortilla is their prisoner.
When the bandits continue their pursuit, Grey tells Bill to pilot the Enterprise at night rather than risk putting ashore. Bill points out the dangers of traveling in the dark and they flip, and Grey wins the toss. Grey goes back to tell Winslow and Lucy that they'll arrive at Chicota Landing the next morning, ahead of schedule. The Enterprise suddenly hits a sandbar, and the crew prepare to defend the ship. Lucy wants a gun but Grey refuses to give her one and has Winslow take her to a cabin for her own protection. Bill confirms that the hull is intact and they have Carney bring the boilers up to full steam. Going in reverse, they pull free of the sandbar. However, Joshua checks on the prisoner and tells Grey that Cortilla has escaped. They check the prisoner's cabin and confirm that the support post broke off in the collision. However, there's no sign of Cortilla aboard the Enterprise.
The Enterprise arrives at Chicota Landing the next morning and Grey confirms that there are soldiers on the dock waiting to transfer the gunpowder. However, when they dock, Cortilla and his men step out of a nearby cabin. Grey and the crew realize that the soldiers are bandits in disguise, and Cortilla freely admits that he killed the original men. Furious, Winslow lunges at him but the bandit easily club him down. Cortilla takes Lucy hostage and tells Grey that they're going to put the gunpowder on the bow of the Enterprise. He then plans to sail it back and ram the ship into the Taylorsville dock, destroying the town. When Grey refuses to take Cortilla there, the bandit orders his men to shoot Carney. Grey give in and Cortilla escorts Lucy aboard.
Once the Enterprise leaves Chicota Landing, Cortilla forces Grey to set course for Taylorsville. When La Carniceria tries to take Grey's pocket watch, the captain fights him and soon knocks him down. The other bandits hold him down and Cortilla comes to see what happened. When Grey explains, Cortilla takes the captain his to his captain and warns him that he saved his life. If Grey had stayed on deck, La Carniceria's friends would have killed him. Grey figures that Cortilla needs him alive to pilot the boat, but the bandit leader explains that he needs Grey to perform another function as captain: wed Cortilla and Lucy. Once they are married, Cortilla plans to return to Mexico with his bride, carve out an empire, and make her his empress.
Grey refuses and Cortilla has his men bring Winslow in. The lieutenant tells Grey that Cortilla is bluffing, but Cortilla shoos him in the shoulder and warns Grey that the next shot will be fatal. Grey agrees to perform the wedding then asks what will happen to his crew when they arrive at Taylorsville. The generale says that will put them ashore rather than risk an untimely rebellion. Once he's done with Grey, Cortilla goes to Lucy's cabin and tells her that they will be married that night.
Up in the pilothouse, Grey has Bill confirm that they're a few mile away from the sandbar they hit on the first leg of their trip. He then calls Carney to check on the "deadwood," and the stoker confirms that there are two bandits watching the boiler room. Grey tells Carney to attack on them signal and then tells Bill to head for shore. Meanwhile, he'll lead off some of Cortilla's men and reduce the odds against them.
Grey goes to see La Carniceria and asks to see Cortilla. However, Cortilla has realized that they're heading for shore and plans to shoot Grey. The captain warns that the sandbar is ahead and an impact with it could set off the gunpowder. Despite that, Cortilla refuses to let the Enterprise tie up on shore. Lucy, listening in and realizing Grey's plan, jumps overboard and swims to shore. Cortilla reluctantly tells Grey to take the Enterprise to shore but has his men lock the riverboat crew up in the cargo hold while he sends two bandits to search for his bride-to-be.
Two hours later, Grey waits with his crew. The bandits haven't returned, and Grey admits that he doesn't know what to do. Carney is ready to rush their guards and Grey reluctantly agrees. However, La Carniceria comes in and take Grey to Cortilla. The generale figures that Lucy was working with Grey to force them ashore. Grey suggests that she jumped overboard rather than face marriage to Cortilla, and the generale slaps him. He has La Carniceria and two men take Grey ashore to execute him. However, Grey throws dirt in their eyes and runs into the forest.
The bandits split up to find Grey, who doubles back and attacks La Carniceria. Once he knocks the man out, Grey takes the thug's gun and swims out to the Enterprise. He climbs the paddle wheel and then goes to the pilothouse to call Carney and the others. They're relieved to hear that he's alive, and Grey tells them to rush the guards when they hear a gunshot.
Grey goes to the deck and prepares to shoot Cortilla. The generale spots Grey and ducks for cover, while the Enterprise crew attack the bandits. After a brief fight, they subdue their captors. However, Cortilla gets to the gunpowder and threatens to set it off, killing himself and everyone aboard rather than go back to prison. Bill shoots him with a rifle, wounding him, and Grey restrains Cortilla before he can shoot the barrels. A few minutes later, the bandits return with Lucy and the Enterprise crew easily capture them.
The Enterprise arrives at Taylorsville the next day and Matson comes aboard to collect his prisoner. The sheriff says that the townspeople have calmed down and built him a new jail to replace the one they burned down. Bill asks if it's the same as the original. When Matson says that it is, Grey tells him that he's going to have a housing problem and has his men march out all of the captured bandits.