In
Beverly Hills, California, wealthy businesswoman Vivian "Viv" Ashe leaves her richly pampered pet
chihuahua, Chloe, with her irresponsible niece, Rachel, while she embarks on a business trip for ten days. Papi, the landscaper Sam's pet Chihuahua, has an unrequited crush on Chloe, which she is annoyed by, as she is unable to put up with his quick wit and unorthodox lifestyle. On a whim, Rachel decides to go to
Mexico with her friends and brings Chloe along. When Rachel leaves Chloe alone in the hotel room to go dancing at a club, Chloe goes looking for her, but gets dognapped as she tries to find Rachel and is sent to the dog fights in
Mexico City. There, she meets a street-smart
German Shepherd named Delgado. Rachel comes back to the hotel and is frantic when she finds Chloe missing. Chloe is picked to fight in the pit against El Diablo, a fierce Argentinean-Bolivian
Doberman Pinscher. Delgado helps her escape the dog fights, unleashing the other dogs from their cages and unlocking the ring to allow both Chloe and himself to flee. After several arguments, he then decides to return her to Beverly Hills safely. Meanwhile, Rachel and Sam go to the Mexican police and offer rewards in an effort to find Chloe. El Diablo is sent by the dog fight ringleader, Vasquez, to capture Chloe. Chloe and Delgado split up when Delgado goes to get help to return Chloe to Beverly Hills. While he is gone, Chloe saves a
pack rat named Manuel from being eaten by an
iguana named Chico. Manuel gratefully offers to take Chloe's collar to a ship for the captain to read it, and Chloe accepts. When Delgado returns and finds out what happened, he explains that it was all a con to steal Chloe's expensive collar, and that in reality, iguanas are vegetarians. The dogs reach the border by train, but they're caught when the conductor of the train wanders back to the place they and the other dogs are hiding. They're forced to jump out, eventually arriving in the barren deserts of
Chihuahua, where Delgado explains that he was a former police dog; he was retired after he lost his sense of smell during a raid and a sneak attack from El Diablo. Chloe and Delgado are attacked by a group of
mountain lions, but are rescued by a group of Chihuahuas led by a long-haired Chihuahua named Montezuma. Montezuma teaches Chloe that Chihuahuas are a "tiny but mighty" breed, and tells her to find her bark. He offers to let Chloe stay with them, but she declines, saying that someone is waiting for her at home. She realizes Papi meant well (even if his approach needed work), and regrets not giving him fair a chance or settling their differences. Rachel and Sam are in
Puerto Vallarta and find that Chloe was spotted in the state of Chihuahua. After tracking Chloe and Delgado from Mexico City, El Diablo arrives in Chihuahua and attempts to capture Chloe. Papi saves her and ends up getting captured in a cage inside an abandoned Aztec temple. Delgado encounters Manuel and Chico with Chloe's collar, and Manuel frantically explains that they wanted Delgado to smell the collar to find Chloe. Delgado responds that he can't, but Manuel convinces him to try. Delgado smells the collar, and is finally able to track Chloe's scent; taking the collar with him. Chloe rescues Papi, but Delgado discovers that El Diablo - in turn - attempts to attack; yet Delgado defeats him. Rachel finds Chloe with the two happily reuniting, and Vasquez is arrested by the police while El Diablo manages to escape. Chloe returns safely to Beverly Hills without Vivian finding out what happened and accepts trying a romantic relationship with Papi, as well as Rachel with Sam. The characters' fates are later revealed: Delgado returns to being a police dog in
Mexico; El Diablo is eventually recaptured by Delgado and is adopted by a rich lady who "had a passion for fashion"; Chico and Manuel move to
Beverly Hills and become rich; and Papi and Chloe have their first date. ==Cast==