The Monkees' second season opener finds The Monkeemobile breaking down in the backwater Mexican town of El Monotono. While Lupé, a mechanic, looks the car over, the boys enter Pedro's Café, where, while ordering, Davy becomes smitten with Angelita, the pretty waitress. Her father Pedro, the cafe's namesake proprietor, insists he mustn't see Angelita and that they must leave town at once. José, a bandito, reports that Angelita is the woman of El Diablo, AKA The Bandit Without A Heart. José throws a knife at The Monkees table, sending them stacking up their chairs and scurrying out into the street.
Davy tries to go back into the cafe to see Angelita, but José intimidates them once more with the knife. Checking on the progress of their car, Lupé tells them that the whole engine needs to be replaced, costing $14.95. To earn the money, The Monkees persuade Pedro to hire them to do a show for the cafe and the concert is a huge success, featuring the new tune "What Am I Doing Hangin' 'Round?" After Pedro pays them, they all plan to skip town right away until David spots Angelita again and insists against his mates' wishes on saying goodbye. He bids her farewell though Angelita explains that she doesn't want to be El Diablo's woman but no one has much choice in El Monotono. Soon she and David are locked in a kiss just as a man storms in announcing that El Diablo and his bandits are on their way, causing the patrons to run away in fear.
El Diablo and his horde of banditos barge into the cafe causing a ruckus with their shooting and witnesses Davy and Angelita still engaged in their goodbye kiss. He begins humiliating Davy by shooting at his feet to make him dance then forces him at gunpoint to beg for his life on his hands and knees. The other Monkees briefly join in until El Diablo frightens them back with his gun. As he degrades him to Angelita, she still declares her love for him anyway and starts displaying affection for him further rousing the bandit's ire. El Diablo then has his minions drag Davy to their camp while the other Monkees watch helplessly. The other guys attempt to intervene but their fear of El Diablo quickly discourages them.
Micky tries to get help from the townsfolk by making a moving speech about standing up for themselves but it backfires when he insists they go to El Diablo's camp and confront the bandits, which causes everyone to flee. Then Micky, Michael and Peter decide to disguise themselves as Mexican bandits complete with fake mustaches and, after paying Lupé for the repairs to The Monkeemobile, set out to rescue their friend. As Davy stands tied to a tree guarded by one of El Diablo's underlings, the trio barge into the bandito camp firing their guns into the air, but the bandits aren't stirred up by their pretense. Only when the guys lower their guns, the bandits surround them at gunpoint.
José has The Monkees taken to El Diablo in his tent. There, they present themselves as El Dolenzio (The Bandit Without A Soul), El Nesmito (The Bandit Without Any Conscience), and El Torko (The Bandit Without A Nickname), and suggest joining forces. Not impressed, El Diablo proposes a series of tests, but warns of the consequences should they fail. First there's a test of strength in which El Diablo and Michael arm wrestle and Michael wins by inadvertently knocking the former senseless with a board. Second, a test of skill and determination involves El Diablo and Peter playing cards (Go Fish) and smoking cigars, and Peter defeats him. Finally, a test of bravery has the bandit and Micky engaging in combat by grabbing the end of a small rope while trying to knife each other, and Micky wins by slashing the rope and sending the bandits tumbling to the ground. Later, Micky, Michael and Peter, having successfully met every challenge by using their wits, celebrate with the bandits by drinking booze, but the guys actually spill their drinks on the ground. While the bandits get drunk, Michael sends Peter off to find Davy. When El Diablo questions Peter's departure, Michael and Micky allay his suspicions by saying he needs some fresh air after consuming a great amount of wine.
A short distance away, Peter arrives to rescue Davy trying unsuccessfully to get the guard to leave for the party who doesn't understand English until Peter says the word booze! At first, Davy is fearful not recognizing Peter, then he tries to get him to untie him but Peter can't undo the rope binding his wrists, as it is tied in a square knot. Meanwhile back at the party, Micky gets caught up in the celebration as he dances on the table to keep the bandits amused ("I'm just trying to mingle!") and Michael has to persuade him to leave with him to find the others. Using the same excuse for Peter's departure, they head off. When they do arrive to where Davy and Peter are, Peter is still trying to untie Davy and Micky effortlessly undoes Davy's bind ("You just put the loose end through the figure 8!"). Then they jump into The Monkeemobile planning to drive off but are stopped quickly by a Mexican parking attendant who charges them $0.50 for parking and having done so, the guys respond by running over his toe driving off.
When El Diablo sees that David and the others are gone, he realizes they've been duped and sends his chief bandito José after them. It isn't long before The Monkeemobile runs out of gas, forcing The Monkees to push her back to El Monotono. Lupé the mechanic offers to provide them with gas, and David rejoins Angelita. Just then, El Diablo's bandit rides into town to deliver an ultimatum to Micky, "the musician who claimed to be El Dolenzio". Micky reads the message that states that El Diablo has challenged him to a duel of honor at the center of town at high noon. At first Micky and the others prepare to flee until Angelita insists that El Diablo will take his anger out on the townsfolk should Micky not show up for the showdown.
Later in the cafe, Micky, now dressed in a white cowboy outfit, prepares for his showdown with El Diablo as Davy, Peter and Michael help him with his gear. When the clock strikes high noon, Micky confronts El Diablo and after advancing towards each other, El Diablo orders him to draw on the count of three but El Diablo cheats by drawing on the count of two instead and fires on Micky repeatedly. However, Micky taunts him on missing him making silly faces and then, as they sing "What Am I Doing Hangin' 'Round?" The Monkees and the bandits engage in battle which ends with them roping the banditos and winning the fight, while Davy once again kisses Angelita.