Five-year-old Luong Ung is the second youngest child in a large and prosperous family, and she lives a happy life in Phnom Penh. In April 1975, her world is abruptly upended when trucks of soldiers roll into the city, greeted by cheers from many of its residents. The Ung family hastily packs to leave, finding nothing to celebrate in the arrival of the destructive force. The soldiers are Khmer Rouge, a communist group under the leadership of Pol Pot, and they have won the civil war raging in Cambodia. They announce that the Americans are coming to bomb the city and insist everyone must evacuate. Leaving most of their belongings behind, the Ungs climb into their truck and join the mass exodus. This is the beginning of a multiyear ordeal under the cruel Khmer Rouge regime, which will claim the lives of four of the family’s members. 

The family drives, then walks, to Bat Deng, Ma’s home village, where her brothers live. They are not safe there, however, and move again several times before finding a village remote enough to protect their identity. Conditions in Ro Leap are difficult and made worse by the Khmer Rouge’s policies, which are designed to establish their "ideal nation", Democratic Kampuchea. The Ungs, along with most others in the village, are soon starving. Forced to labor endless hours with insufficient rations, the Ungs do whatever it takes to survive. For example, Kim, the youngest Ung brother, endures beatings in the house of the village chief to acquire extra food.  

As the state’s demands increase, the family’s situation becomes increasingly precarious. Like many in Cambodia, starvation haunts their every step. The parents arrange a marriage for their second son, Khouy. This protects him from conscription, but both he and Meng, the oldest son, are sent to a work camp. Several months later, the family’s oldest daughter, Keav, is also sent to a work camp. She becomes mortally ill and dies before Ma and Pa can travel to care for her. Before the family can mourn, the Khmer Rouge take Pa to one of the infamous Killing Fields, where he is likely executed. With the death of Pa, Luong loses her emotional anchor, and the family its best protector. 

Kim takes over as head of the family and risks his life stealing corn from a nearby field. After he heals from the Khmer Rouge’s brutal beating, Ma decides that he, Chou, and Luong must leave in order to survive. They don't want to, but they acquiesce, although Chou and Luong stay together against Ma’s instructions. The girls go to a work camp for orphans, and soon Luong is sent to a camp for stronger children, where she is trained as a soldier. She visits Ma once and is horrified to see how frail Geak, the youngest Ung child, is. Later, Luong falls ill and is thrilled to meet her family at the local infirmary. They spend nearly a week together, laughing and caring for one another, before overcrowding drives them apart again. This is the last time they see Ma. 

Back at the camp, Luong has a terrible premonition and sneaks out to return to Ro Leap. When she arrives, a neighbor tells her that soldiers took Ma and Geak away. Traumatized, Luong stumbles back to the camp, and she never remembers what happens in the three days that follow. She pours her grief into her training, savagely attacking dummies that she imagines are Khmer Rouge soldiers. When the Vietnamese invade Cambodia, she takes the opportunity to escape and runs in search of Chou. She finds Chou and their brother Kim, and the three head to a refugee camp. Without parents, they struggle to survive, until a foster family takes them in. Their first foster family is cruel but their second is more welcoming. A surprise attack by the Khmer Rouge reminds them that the danger is not over. 

They are beginning to worry about finding a new foster family when Kim runs into Meng. All the remaining siblings are reunited and decide to return to Bat Deng, Ma’s home village. As the head of the household, Meng agrees with Ma’s brothers that he should marry, and they choose a woman named Eang for him. After a few months, Eang’s sister arrives in Bat Deng with the news that their family fled to Vietnam when the Khmer Rouge entered Phnom Penh. Eang and Meng travel to Vietnam, but Meng returns in a few days with a plan to travel through Vietnam to Thailand, and then on to the United States. The voyage will be difficult and costly but, after five years in America, he will be able to reunite the entire family. Meng decides that as the youngest, Luong is the most likely to be able to make a good life in a new country, and the two leave on bicycle. 

In Phnom Penh, Meng books passage for he and Luong on a fishing vessel to Vietnam. The bustle of Saigon amazes Luong, who misses her siblings but is excited by the prospect of a new life. They remain in Vietnam for several months, first in Saigon then on a houseboat on the Mekong Delta, until the arrangements for human smugglers to take them to Thailand are complete. When they finally cross, the journey is perilous, with both storms and pirates menacing the refugees. Luckily, they survive and arrive at Lam Sing Refugee Camp. As they wait for sponsors, Meng converts to Christianity to increase their odds, and they worry about how to find sufficient food. At last, they learn that they have a new home in Vermont. The memoir ends as Luong boards the plane, having dreamt about Pa. A brief epilogue shows Luong returning to Cambodia as an adult and reconnecting with her family.