Jim, Artie, and a Federal marshal ride out to intercept a stagecoach as it makes its way through the countryside. They see a woman passenger inside with a male passenger and figure that the driver and his partner riding shotgun took on the women to look convincing. The three men ride down and order the driver to halt. He does so without putting up a fight and asks what is going on. The marshal presents a warrant to search the stage and says that they’re looking for boll weevils. The shotgun man opens fire, wounding the marshal, and Jim tackles them. The marshal shoots the driver, Artie takes on the male passenger who ends up shooting himself in the struggle, and Jim captures of the shotgun man. Artie opens the door for the woman, who falls out, revealing that “she” is a mannequin. The head falls off and the agents confirm that there are hundreds of boll weevils inside.
The marshal assures the agents that he can get back to town and rides off. The driver denies knowing anything about the boll weevils, and Jim draws a gun on him and forces him to tell the truth. The man says that he picked up the stage in Sausalito and was heading to the small settlement of Mesquite. When he gets to a fork in the road outside of Mesquite, caballeros pick up the stage and send the driver on ahead to wait until he hears from them again. He then picks up the stage and drives back. Someone named Cass hired him in San Francisco, and Jim rides to the fork in the road while Artie goes back to San Francisco, drops off the driver with the police, and tries to find Cass. As Artie puts the mannequin back into the stage, he sees a manufacturing company label for Far Western on the foot.
In San Francisco, Artie meets with James Jeffers, the commissioner of the California Department of Harbors. Jeffers assures Artie that all ships will be searched for boll weevils and wonders if the government believes that he’s been lax. Artie assures him that he’s been thorough, but that it’s difficult to find boll weevils. He explains that they can decimate a field of cotton in a single day, and at the current rate of infestation they could destroy every cotton field in the U.S. They had a tip about the Sausalito stop and Artie asks if he knows a man named Cass. Jeffers recognizes the name as Tom Cass, one of his harbor supervisors, and has him summoned to his office.
Jim takes the stage to the fork and several caballeros stop him. He claims that the regular driver is sick and Cass hired him to take the man’s place, and that Cass sent the other stage as a decoy. When Jim offers to explain to the man’s boss, the leader, Jon, assures him that no one gets to the boss and tells Jim to meet them tomorrow to pick up the stage and take it back. Once the agent rides off, Jon tells one of his men to follow him and make sure he gets to Mesquite. Jim ducks off the road and then ambushes the caballero when he rides by and orders him to say where the stage is going.
Jeffers informs Artie that Cass has disappeared, abandoning his office and home. He apologizes for losing Cass and Artie understands.
Jim rides into Mesquite, wearing the thug’s sombrero and poncho. As he tries to make his way inside, a man figures him as an intruder and stops him at gunpoint. Jim knocks him out and goes inside a townhouse, making his way to an elaborate set of doors. However, a burst of gas shoots out of the knockers and Jim staggers in to the parlor. An Arabic man and woman look on as Jim collapses.
When Jim wakes up, the Arabic man, Abdul Hassan, has him tied up and congratulates the agent on making it so far. Jim readily tells him that he’s with the Secret Service rather than try to bluff it out, but asks Hassan to indulge him by explaining his plan. Hassan readily agrees and explains that he’s a distributor and shows off a map indicating his chain of operatives who move the weevils further and further inland to the South. Once the cotton is destroyed, Hassan and his syndicate will move in, having gained control of other major cotton supplies. He then shows off two separate tubes containing two larger weevils and tells Jim that they are bred to feed on wheat, corn, and barley. Hassan leaves with the woman, Fatima, after telling his men to dispose of Jim as quietly as possible. When the thugs prepare to decapitate Jim, he fights back, breaks his bonds, and knocks the four men out. Caballeros hear the commotion and come to investigate, and Jim grabs the map, bars the doors, and climbs up a ladder to the roof. He then fires a line across the street and drops down onto a horseman, takes his horse, and rides off.
Artie goes to Tucker’s Landing on the San Francisco wharves and finds the Far Western manufacturing company. Upon discovering that the door is locked, Artie goes up to a second-story door and breaks in. The warehouse is filled with mannequins... and Cass’ corpse, dangling among the dummies. Tucker comes in behind Artie with a gun and demands to know why he’s there, but Artie cuts down a rack on the man and makes his escape.
Later, Jeffers tells Artie that the warehouse is a legitimate business and by the time his men searched the place, there was no sign of Cass’ body. Jim arrives and tells them about Hassan. He shows them the map and Artie goes to wire the information to Washington. Jeffers’ daughter Betsy comes in and hopes that her father has been helpful, and then asks her father to fill out a credit application for her. She invites them to dinner at their house and Jim accepts, but Artie says that he has another engagement. Outside, Jim wonders why Artie is giving him a clear field with a woman. His partner says that Tucker’s lobster boat has a shallow draft flatboat, which would only be useful if Tucker was going up a shallow river. Artie plans to check it out that night.
At the Wanderer
, Artie sends the wire to Washington and goes over his portfolio of disguises to come up with a new one. Jim is busy reading up about weevils and then tells Artie that he’ll check in with him later. Artie is soon back at Tucker’s Landing disguised as an elderly fisherman. He settles down on the dock to eat his lunch and sing, and points out that Tucker is taking a shallow-draft boat out into deep water. Tucker tells him to leave but Artie points out that they’ve got hidden lights. When Tucker draws a knife on him, Artie reluctantly moves on.
Jim tells Jeffers and Betsy about how Hassan got away, but assures them that they’ve intercepted Hassan’s operatives. As they talk, men break in and attack the butler. Jim hears them and runs out, and more men break in, knock out Jeffers, and abduct Betsy. When Jim runs in, they knock him out and escape in a carriage.
Jim meets with the disguised Artie at the docks and brings him up to speed. He followed the carriage to the waterfront and figures that they’re coming to Tucker’s Landing. Tucker’s man Ringo arrives in his lobster boat and Artie explains that he’s been covering up his running lights with oilskins. Tucker tells Ringo that they have Betsy. Jim and Artie see the exchange and Jim goes along the pier and below the docks while Artie tells one of the guards that someone has been tampering with the floats.
Tucker and his men take their boat beneath the warehouse and collect a mannequin. Jim watches them and then dives into the water to swim after them and then grabs the back of the lobster boat and lets them unwittingly tow him along. They go out to a channel marker and remove a tube filled with weevils, and put them into the mannequin.
On the dock, Artie approaches a guard at the warehouse and gasses him unconscious with a trick pipe.
Tucker and his men row to shore where a stage is ready to take delivery of the mannequin. Jim slips around and boards the stagecoach, and then grabs the driver’s gun and tells him to drive to the Presidio police station.
Artie removes his disguise and enters the Far Western warehouse. He finds Betsy beneath a tarp and wakes her up, but armed men come in. Artie tries to bluff it out without any luck.
Jim goes back to see Jeffers, who says that he’s received a ransom note demanding that they give up the investigation. The agent refuses, saying that he’s under orders from Washington, and assures Jeffers that he’ll get Betsy back. He then goes to the Far Western warehouse and enters from below. Tucker and Ringo are waiting for him, and Jeffers comes in and welcomes Jim to the club.
Once both agents are tied up, Jeffers tells them that Betsy doesn’t know anything about what he’s up to. Jim warns him that Tucker will tell Betsy the truth, but Jeffers figures that he can order Tucker to burn down the warehouse and then shoot him and rescue his daughter. Tucker and Ringo return and overhear Jeffers and shoot him dead. Ringo figures that he can burn down the warehouse just as Jeffers planned, go to New Orleans, and renegotiate with the syndicate. He sends Tucker to get Betsy next door at Tucker’s Landing, starts a fire, and leaves. Jim extends his boot knife so Artie can cut himself free. Artie rescues Betsy while Jim follows Tucker.
Tucker meets with Hassan and they share a toast to their new venture. The Syndicate man shows him the two breeding weevils. Meanwhile, Jim knocks at the door and attacks Hassan’s men when they answer. He fights his way in and takes on Tucker and the thugs, while Artie arrives just in time to knock a gun out of Hassan’s hand. Once everything is under control, Artie tells his partner that he broke the news to Betsy, and they collect the weevils.
Later, Artie is at the Wanderer
entertaining his date, Joanne, when Jim comes in with his date, Mary. Jim shows them the weevils, Samson and Delilah, and decides to let them breed before being dissected for testing in Washington. The women are drawn to the romance of the breeding weevils, much to Jim’s amusement and Artie’s disgust.