Mia, a 35 year-old successful photographer living in Paris, finds herself suffering from a typical bourgeois malaise, seeking solace in cocaine. Looking for a fresh start and inspiration, she flies to Cambodia to surprise her timber trader husband Xavier, and hopes to create the child for whom she longs.
Instead of finding a warm welcome at the hotel, she discovers Xavier in a seedy brothel having sex with a little girl, Srey. Mia faints in shock. When she comes to her senses, she wanders through the slums in a daze, shaken by the exploitation of both young boys and young girls.
Mia resolves to right the wrongs she has witnessed and saves Srey from Sanan, Srey's pimp. She cashes as much money as she can, but it's still not enough to buy the girl's freedom. Sanan offers Mia an alternative bargain: it is only by surrendering her own body to Sanan's client, a high government official, that Mia manages to attain Srey's release, but this sacrifice leads to the return of her cocaine addiction.
On the way to Srey's home deep in the jungle, Mia discovers that two other little girls from the brothel, Daa and Malin, have hidden in the back of her truck. Srey also discovers that the girls stole money from Sanan, the pimp. Mia reluctantly takes on the responsibility of returning all three girls to their far-flung villages, knowing she's now in deep trouble with Sanan and must keep off the main road.
Meanwhile, Xavier, who is unaware Mia had witnessed his crime, cannot understand why Mia is not returning his calls. Fearing she has relapsed into her drug habit and is in trouble, he contacts the police, as does Sanan, who tells a corrupt official Mia stole the girls from him. Police officer, Munny, is set on Mia's trail.
During their long trek, little Daa falls ill. Desperate, Mia carries her to her village just in time to hand her to her family before the little girl dies of septicemia in her mother's arms.
A Buddhist funeral follows in an ancient temple. It is here that Munny finally catches up with Mia. He arrests her, but soon realizes that, far from harming the little girls, she is in fact helping them. That night, wrestling between conscience and his own future, the policeman Munny lets Mia go.
Mia, Srey, and Malin's trek continues up the river to Malin's village, built of huts perched on stilts rising from the water. Their excitement grows as they come closer and Malin cries out for her mother. But the longed-for reunion is cruelly rebutted as Malin's mother refuses to take back her daughter and she turns the boat away.
They continue their journey to Srey's village, travelling up the wide and calm Tatai River by canoe. Entering the jungle, Mia struggles to keep up and finds herself dependent on the girls she is meant to be saving. Suffering from withdrawal and exhaustion, the relationship grows tense and jealous between Mia and Srey each needing the other, having been brought together by the man they have both known sexually. Each must draw on the other's strengths and endure rejection to enable themselves to find peace and sanctuary.
When they finally reach Srey's village, Sanan is there waiting, and Mia must face a violent and bloody confrontation to save the girls and herself.