Jim, Artie, and a U.S. Marshal man intercept a stagecoach and say they're searching for boll weevils. The driver and guards put up a fight, wounding the marshal. Jim and Artie capture the others and they open the stagecoach only to find that the female passengers are… mannequins, filled with rice and boll weevils.
The marshal rides back into town while the stagecoach driver says he doesn't know what he was carrying. Under threat, he admits he was heading for the small settlement of Mesquite and has made the trip before. He admits a man named Cass hired him in San Francisco. Artie heads back to San Francisco to find Cass while Jim rides ahead to Mesquite. As Artie loads up the mannequin, he notes a manufacturer's tag on its heel and pockets it.
In San Francisco, Artie meets with James Jeffers, Commissioner of the Department of Harbors. All ships arriving are searched for boll weevils, and Artie warns that they can devastate a field of cotton and someone is using them to eliminate the U.S.'s cotton supply. Jeffers identifies Cass as one of his harbor masters and they order him to be brought in.
Jim drives the stagecoach near Mesquite where the men want to know who he is. Jim covers as best as he can. The leader tells Jim to continue on to Mesquite on horseback and they'll meet him the next day to give him the stagecoach back. After Jim rides off, the leader tells one of his men to make sure Jim gets to Mesquite. Jim captures the man following him and demands to know where the stagecoach is.
Jeffers reveals that Cass has disappeared while Jim rides into Mesquite wearing a poncho and sombrero. He takes out a guard and goes in, only to get a faceful of gas from a door. He collapses into a luxurious Arabian-FORBIDDENroom and passes out.
When Jim wakes up, the room's owner, Abdul Hassan, wants to know who he is. Jim identifies himself and Hassan reluctantly admits he must kill him. Hassan boasts about his weevil-smuggling operation, and shows off a container holding two specially-bred boll weevils capable of feeding on other plants besides cotton. Hassan leaves and tells his guards to dispose of Jim, who starts a fight and takes out the guards. Jim heads to the top of the building and uses a harpoon-and-wire gun to head down to the ground, steal a horse, and make his escape.
Artie goes down to the docks and checks out the factory where the mannequins are made. Among the dummies Tom finds Cass' corpse. A thug gets the drop on him but Artie drops a rack on him and gets out. He meets with Jeffers who reports the businesses are legitimate and there's no sign of Cass' body. Jim shows up to report about Hassan and Jeffers' daughter Betsy arrives. She offers them a sightseeing tour and then dinner that evening, and Jim accepts while Artie pleads another engagement. Later he notes that the factory owner has a shallow-bottom boat that could be used to go up-river.
At the Wanderer, Artie is going over his file of disguises and comes up with a new one to check out the docks. He asks about the shallow-bottom boat and attracts attention of a thug who chases him off. Jim tells Jeffers and his daughter about his mission with Hassan. They're interrupted when men break in, knock out the doorman, and leave out the front. Jim comes in to find other men trying to grab Betsy. They knock Jim down long enough to escape and put Betsy into a carriage and leave.
Jim follows the carriage to the waterfront but loses them. He briefs Artie on the situation and Artie has spotted where the boat's going into a secret channel. Artie creates a distraction while Jim checks out underneath the factory and finds men loading a mannequin. Jim dives in and secretly latches on to the back of the boat to follow them. They row out to a buoy where they pull out a tube and put the weevils into the headless mannequin. Artie pokes around the docks near the factory and knocks out a guard with a smoking pipe rigged with gas.
Jim follows the mannequin to a stagecoach driver heading to Fresno. Jim hijacks the shipment and directs it to the police station. Artie gets into the warehouse and finds Betsy, but several men get the drop on him.
Jim reports to Jeffers, who has a ransom note telling them to drop the case or Betsy will be killed. Jim refuses and goes to the mannequin factory, where the guards hold him at gunpoint… and Jeffers comes in. After having Jim tied up, he boasts that Betsy knows nothing and will have his main man, Tucker, burn the factory down because the guy is disposable. Turner overhears him and is none too happy, and shoots Jeffers. He takes over Jeffers' plan and sets the factory on fire before departing. They free themselves with Jim's boot knife and go after Tucker, who is meeting with Hassan. Jim takes on the guards and disposes of them, Artie arrives to clean up, and they take the weevils into custody.
Later on the Wanderer, Jim and Artie are meeting with a couple of attractive ladies. Unfortunately they're more fascinated by the boll weevils than with the guys.