Maurice Chevalier is rehearsing in his hotel suite. The Ricardos are next door, arguing about Lucy wanting to go shopping in Tijuana, Mexico. Next door on the other side, Fred and Ethel are arguing as well about her wanting to go shopping. Maurice resorts to wearing a pair of earmuffs during his rehearsal. Lucy and Ricky continue fighting and are interrupted by Little Ricky and then Maurice announcing they are ready for the dress rehearsal. Lucy tries asking Maurice whether he'd let his wife go shopping in Mexico if he were married. Not wanting to be involved in the Ricardos' dispute, he tries making a hasty exit--but not before Lucy accidently damages his hat. Trying to keep himself calm, he begins counting--a technique he uses anytime he is in an upsetting situation. Ethel and Fred come in with Ethel trying to wheedle money out of Fred, but he refuses. Maurice mistakenly suggests that the girls come and watch the rehearsal. Lucy decides that this would be a good idea, harboring the notion that she could do a duet with Maurice. Ricky promptly "pays off" Lucy by giving her spending money to go to Mexico and gives her twenty dollars. Ricky tells Fred to pay up as well, and asks him to keep an eye on the girls and buy a dozen maracas for the show for that evening.
Fred and the girls arrive in Mexico and are stalled in traffic, thanks to a donkey. In the midst of the traffic jam, they meet a Mexican boy named Alfredo, who begs Lucy to let him come with her so he can board an aircraft carrier when he learns that she has to get back to Ricky's performance (it is going to be aboard an aircraft carrier). She tells him that she can't take him. When the policeman approaches, Alfredo runs away. Moments later, the girls go shopping and end up with armfuls of packages--and an exhausted quota from buying Maurice Chevalier's French perfume. Alfredo reappears and loads Lucy and Ethel's things into the trunk. Before he leaves, he begs Lucy once again to take him with her. She again refuses and asks him to close the trunk. He does so, but sneaks inside the trunk. Fred urges the girls to get ready to go to the hotel to get his free lunch, so the girls go through Customs. While there, the police officer asks to see the items Lucy and Ethel have purchased. After fishing deep in her purse, Lucy finally produces the trunk key and hands it to the police officer. He opens up the trunk only to discover Alfredo inside. Alfredo runs off and the girls deny any knowledge of his being in the trunk, so the police officer quickly detains Lucy and the Mertzes.
Meanwhile, during dress rehearsal, Maurice, Ricky and Little Ricky perform "Valentina." Lucy calls and tells Ricky that she and the Mertzes are being detained at the border patrol office for smuggling; Ricky goes through the roof and later goes down to the border office to contact the admiral, who grumpily vouches for the trio. The police officer releases them. Ricky says that he'll drive the girls and instructs Fred to drive Maurice, who is asleep in the car. Lucy, realizing that she now has two extra quotas from Ricky and Maurice, tries convincing Ricky to let her buy a cashmere sweater, but he refuses. She explains that she couldn't because her quota was used up when she bought Maurice's perfume. Ricky insists that they get a move on so they rehearse the fiesta number, which prompts Fred to announce that he's forgotten to buy the maracas. Disgusted, Ricky, Fred and the girls leave to do some last-minute shopping.
Maurice wakes up from his nap and is stunned to find out that he's in Mexico-his visa forbids him to return to the United States if he leaves the country. He begins counting slowly in French. Anticipating a delay, Ricky gives Lucy the key to his car so she can park it in front of the store and save time. Maurice heads out to the car. When Maurice gets to Lucy's car, he discovers Alfredo hiding in the trunk. Alfredo begs Maurice to let him come to the States with him. Maurice takes Alfredo out of the trunk, but Alfredo tells Maurice that he left his hat inside. Maurice climbs in to get it, but when Lucy backs Ricky's car into hers, the trunk door slams shut, leaving Maurice locked inside. Alfredo frantically tries explaining that Maurice is locked in the trunk, but Lucy, thinking Alfredo is again begging to go with her, asks him to alert Ricky that she'll be waiting for him at the border. In the process of pulling off, Lucy slams into the rear of Ricky's car, and the trunk pops open. Alfredo goes inside the store to tell Ricky that Lucy has just driven away with Maurice in the trunk. Ricky and Fred rush outside and Ricky asks Alfredo to close the trunk. Alfredo sneaks inside the trunk and the boys head to the border.
At the border, Lucy declares the cashmere sweater and the maracas. The border patrolman advises her that she'll have to pay a duty on the sweater, but Lucy explains that she'll be using Ricky's and Maurice's quotas. The border patrolman asks to see the sweater. Lucy gets out of the car and is horrified to discover Maurice tucked away (and counting again) in the trunk. She quickly closes the trunk and Maurice knocks from the inside to be let out. Trying to think of a distraction, Lucy asks the border patrolman to turn off her engine. While he turns off the motor, Lucy opens the trunk and tells Maurice to stop the knocking. The patrolman asks to see the sweater, but discover Maurice in the trunk. Despite being a fan, the patrolman tells Maurice that he's under arrest. Ricky pulls up in the next lane. After hearing that Maurice is being arrested, Ricky offers to go to the border and call the admiral. The patrolman hears Ricky's accent and questions his status as a legal U.S. citizen. The patrolman requests proof and insinuates that Ricky, too, is harboring someone in his trunk. Resenting the insinuation, Ricky promptly goes to the trunk to prove that there isn't anyone in his trunk. When he opens it, he's shocked to see Alfredo inside. Alfredo takes off. At the border office, Maurice, the Ricardos and the Mertzes are detained and the patrolman is unable to reach the admiral. Maurice suggests that they go to see the American Consul. Ricky agrees to go, but the patrolman says everyone else must remain in custody.
Ethel asks the patrolman where she can get something to eat, so he helps her find a sandwich machine. Meanwhile, Alfredo finds Lucy at the border office and speaks to her from outside the window. He offers Lucy a ticket to a bullfight and tells her that the American Consul goes to the bullfights every Sunday. Lucy sneaks out of an open window and heads to the arena. The patrolman, upon discovering that Lucy has escaped, alerts all policemen. At the arena, Lucy manages to evade the Tijuana police and disguises herself as a matador and tries to find her way through a series of bullpens. Back at the border office, Ricky returns saying that he wasn't able to find the American Consul. The admiral once again vouches for the entire group. Ricky notices that Lucy is missing. He nearly hits the roof when he learns that she was spotted going into the bullfights. While trying to look for the consul, Lucy soon finds herself in the actual bullfight. By now, Maurice, Ricky and the Mertzes have all arrived at the arena. Ricky finds the American Consul and asks if he's seen Lucy since she was looking for him. The Consul appears to be more interested in watching the bullfight and says that he is amazed at the redheaded bullfighter. Ricky looks up to find none other than his wife running from a charging bull. He jumps out the stand and calls for Lucy who she heads over to him, ducking behind a wall. Ricky has had his fill of his wife's antics. Maurice, who has witnessed more than his share of them, has traded counting for popping pills.
Back in the U.S., aboard the USS Yorktown, Maurice puts on wonderful show, performing "Mimi" and his version of "Yankee Doodle Boy." Lucy, however, is handcuffed to one of the navy men-on Ricky's orders.