Emily, an old girlfriend of Chad's, appears in Laredo with her father, a railroad tycoon. He offers Chad a $400 a month job, whether the romance between he and Emily works out or not. Reese and Joe try different schemes to bust up the romance but they backfire and Chad proposes to Emily and resigns from the Rangers. Reese and Joe are sent out to protect a wagon train from a possible Indian attack and they use it as one last ploy to keep Chad in Laredo. Reese rides back reporting that the train has been attacked but Chad doesn't believe him. Reese heads back and finds out the wagon train really is under attack, sending a rider back to Laredo. While waiting for the stage with Emily and her father Chad sees Parmalee with other Rangers leaving town and finds out Joe and Reese are in danger. He tells Emily he has to go and will catch up with the stage. She delivers an ultimatum that he must leave right away if he wants her. Chad tells her off, catches up with Parmalee, who reinstat

Reese's inventor friend Major John Cane is called upon to open a locked bank vault. Outlaw Ezekiel Fry sees him do it and tricks him into helping his gang rob the Porfirio Bank. Reese, Chad and Joe are sent to Porfirio to investigate the robbery. Realizing he's been deceived the Major refuses to help rob the Cattleman's Exchange until Fry and his gang kidnap Reese and threaten to harm him. Then Cane invents a precision plan that requires the outlaws to practice their parts in a barn. Chad and Joe follow a dog that has hung around them since they arrived in Porfirio, hoping it will lead them to Reese. Major Cane cuts Reese lose while the outlaws are practicing the robbery and the fight begins just as Chad, Joe and the dog arrive.

Jake Murdock wants revenge on Parmalee for sending him to prison. His plot involves Dr. Duvain who has a mind-controlling drug that can make a man kill his best friend. To remove suspicion they plan to have a ranger kill the captain. Reese is picked and undergoes a series of injections to prepare him for the murder. A $5 gold piece is the key to controlling Reese, whenever he sees one he is to obey the next verbal command which results in Reese allowing an outlaw to escape, immersing himself in a horse trough (Go soak your head) and busting up the saloon. Chad investigates the doctor's background and reads books about chemistry and the brain. He figures out what is causing Reese's strange behavior and convinces Parmalee of it who then devises a way for the plan to backfire on Murdock and the doctor.