Trade

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In a poor family in Mexico City, Adriana (Paulina GaitÃ¡n) celebrates her 13th birthday, and is happy about the bicycle her 17-year-old brother Jorge (Cesar Ramos) gives her. Their mother suspects Jorge has got the money for the present in a dishonest way, and forbids Adriana to ride it. Indeed, Jorge lures a tourist into a quiet street pretending to bring him to a prostitute, and with two friends rob the man by threatening him with guns. After the tourist complies, the three carry out a mock execution, revealing that the guns are only water guns.
About same time, Veronica (Alicja Bachleda), a young woman from Poland, arrives at the airport together with a girlfriend, where they are met by a group who had promised to get them to Los Angeles, but instead they're, in fact, being kidnapped, and when they realize this, in a struggle to get away, the friend is hit and killed by a car.
Against her mother's order, Adriana sneaks out to ride her new bike. When she notices a car following her, she tries to get away, but is captured and taken to the place where Veronica, several Latin American women, and a young Thai boy are also kept. The gang leader pushes Veronica to bed as his henchman begins to videotape. Veronica tries to fight back but is overpowered. As Veronica is being raped, she flashes back and realizes how the traders had conspired and arranged the entire trip, to sell her into sexual slavery.
Jorge sees a boy riding the bicycle he has given to Adriana, suspects that he has stolen it, and stops him. The boy says he has found the bike on the street, and shows the place he found it. Her things still on the street indicate that she was kidnapped. Jorge asks his friends to help him find her, but when an adult adviser tells the boys the kidnappers belong to a powerful globally operating Russian gangster network, they refuse. Jorge finds out that the kidnappers "sell" their victims as sex slaves through a connection in New Jersey.
While Jorge asks people if they have seen his sister, he sees her among the other victims as they are hurried into a truck by the kidnappers. He steals his friends' car and uses it to follow the kidnappers. As he approaches the border, he sees the truck. Two policemen approach the truck and allow them to cross, in exchange for cash and sex. One of the police is allowed to choose a victim to rape, and Veronica is chosen. The gangster evacuates everyone from the truck except for the policeman and Veronica as she is raped again. Jorge manages to follow the van to JuÃ¡rez, but then loses track of it.
Adriana, Veronica and the Thai boy are smuggled into the US, but the group is caught by the US Border Patrol. The gang members keep the kidnapped people from telling the police that they were kidnapped by threatening to harm their families. The kidnappers and victims are sent back to Mexico, after which they sneak into the US again.
When Jorge finally finds the house where the victims were kept, they are already gone. A car with Texas license plates arrives. While the driver Ray (Kevin Kline) looks through the house, Jorge manages to hide in the trunk of the car. He thereby illegally crosses the border into the USA. Jorge reveals himself and tells about the kidnapping, and Ray, a federal insurance fraud investigator, brings Jorge to a police station to report the kidnapping. However, Jorge, who came along reluctantly, flees, suspicious about police. Ray finds Jorge and decides to help him to rescue his sister, and slowly they become friends. It is learned that Ray was in JuÃ¡rez to search for his extra-marital daughter, who was also probably sold.
Jorge and Ray travel to New Jersey, where the victims are being taken and where an internet auction will be held to sell them to the highest bidder. The Thai boy is drugged by an injection in his neck and delivered to an elderly man who buys him. At a rest-stop diner with Ray, Jorge recognizes the little boy, and Ray frees him and forces the man to tell the password of the internet site of the auction.
Adriana is forced to have oral sex with a customer in a field; the gang members tell the customer that he cannot have intercourse with her, because at the auction she has to be sold as a virgin. At a stop, Adriana and Veronica manage to escape. Veronica sees a policeman and tells Adriana to tell him what is happening, while Veronica herself phones her parents in Poland to tell them, but learns that her little son has already been taken by the criminal organization. Adriana fails to tell the policeman, and during the phone call Adriana and Veronica are recaptured by the kidnappers. At another stop, Veronica commits suicide by jumping from a cliff, telling the kidnapper that he will pay for his sins. The kidnapper arrives with Adriana at a house where his female boss keeps more victims. She scolds him for losing Veronica.
Ray and Jorge ask the New Jersey police to free Adriana, but they refuse; it would disrupt their strategy against the larger criminal organization the gang is part of. Ray gets consent by phone from his wife to withdraw a large sum of money from their bank account for a purpose not told to her, and, assisted by Jorge, participates in the auction and "buys" the girl for $32,000, to free her. Ray visits the house where she is kept, bringing the money. However, he asks the female boss (Kate del Castillo) where she is from, making her suspicious. Due to the intense green eye colour and approximate age of the female boss, it is implied that she is Ray's long-lost daughter. He has to prove that he is not a cop by having sex with Adriana in a room in the house. He does not do that, of course; instead Adriana on purpose goes in the washroom and comes back with blood on her hand and smears the bedsheet. The kidnapper comes in to check on them, and understands that in spite of the blood on the sheet they have not had sex. Adriana reminds him of what Veronica said before she died, and in his guilty conscience he cooperates and tells his female boss that the defilement did take place. As they leave, Jorge arrives and hits the man on the head with a tire iron, and the police, checking on the house after all, arrest the two kidnappers and free several children they find in the basement. The money Ray brought is returned to him. He gives it to Jorge, and recommends that he stays out of trouble back in Mexico. Jorge puts the money secretly back into Ray's car when they say goodbye. Jorge and Adriana are flown to Mexico. Adriana is worried that because she disappeared for so long, with no explanation, her mother will be mad, but the mother is just very happy that she is back. Jorge finds the leader of the kidnappers (Pasha D. Lychnikoff) and kills him, but then he is shocked to discover that the man had a young son.

Question: Why did the police refuse to free Adriana?
Answer: It would disrupt their strategy against the larger criminal organization.