New ranger Cotton Buckmeister is assigned by Judge Larkin to return a strongbox of official documents to Uvalde. Chad and Joe are to accompany him. Judge Ike Macallum ruthlessly rules Uvalde and has illegally brought charges against many people in order to blackmail them. So both Macallum victims and his henchmen are after the strongbox. During the journey Chad and Joe discover that Cotton also has an interest in the strongbox as he is ""wanted"" for breech of promise when he refused to marry Judge Macallum's sister Ada. A shootout occurs before Parmalee can arrive with Judge Larkin. Joe ends the gunfight by blowing the strongbox up with dynamite. All of the documents are destroyed except one - Cotton's. Court is held and Cotton is found guilty and Chad and Joe are appointed as supervisors.

Reese and Cotton run off two outlaws intent on forcing the inhabitants of San Diablo to divulge where the fabled treasure is hidden. Dandy Davis is wanted and Cotton heads back to Laredo with him but Dandy fills Cotton's head with stories of the treasure and how Reese will beat him to it. Reese has stayed behind as he knows the other outlaw Ben Slick will be back to raid the town and the San Diablo citizenry has asked him to teach them to defend themselves. Reese becomes general of their ""army"" and is even given a uniform. When the outlaws return Reese and the citizens defeat them and Reese and Cotton are able to return to Laredo.

Murders begin occurring the day Shamus McCloud arrives in town. At first the murder of Doctor Ingram's dog seems to be possible revenge by Shamus McCloud for the death of his brother at the doctor's hands. More murders take place and McCloud is blamed, the believed reason being he is taking revenge on the town too. The Rangers investigate other people who came to town the same day, such as Prof. Smythe and his traveling Museum of Horrors. One of the victims is a gambler that Joe owed money to so even he falls under suspicion. Shamus finally asks to be put in jail so he'll be cleared when the next murder happens. While he is playing cards with Chad and Joe in the jail the three of them figure out the killer is someone who can't tolerate high-pitched noise.

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.

Emerson Whitby III is a millionaire who travels to Laredo to participate in a marathon poker game with other millionaires including the beautiful Sabrina Lane. The Rangers stop an attempt to kidnap Whitby from the stage and discover Whitby and Reese have the same sounding voice. Since the kidnappers didn't see Whitby but only heard his voice the Rangers devise a plan to substitute Reese for Whitby in the poker game. The plan is to let Reese be kidnapped and then follow the gang to their hideout. Reese is captured but puts up too good a fight and Joe, hiding in a bush, has to knock Reese out with his gun butt so the kidnappers can subdue him. The switch is discovered and the real Whitby is spirited away in a trunk. The Rangers rescue him and catch the ringleader when the gang attempts to get the ransom money.

Joe, Erik and Cotton Buckmeister meet printer Lemuel Beamish, who asks to travel with them the next day. Unknown to the rangers Beamish has three men following him. Beamish's cinch breaks and Cotton stays behind with him, spending the night at an abandoned fort. They are attacked and Beamish is killed. Before he dies he recites a nursery rhyme Cotton is to repeat to Beamish's niece when he delivers his belongings to her, which include a satchel of money. The money turns out to be counterfeit and the rangers suspect that the three men and possibly the niece are after something else, such as engraving plates. The nursery rhyme may be a clue to where they are hidden but Cotton can't remember how it goes!

Chad, Joe and Cotton Buckmeister are offered a $50 bonus to transport a bottle of Nitro Glycerin and the Professor who invented it to an army fort. A quick-change artist keeps trying to steal the Nitro and eventually succeeds. The Rangers manage to capture him and get the Nitro back.