After their mother succumbs to a stroke she suffers at a community swimming pool, twin brother and sister receive final requests in their immigrant mother's will. To fulfill her wishes, they must journey to her birthplace in an unnamed Middle-Eastern country (based on Lebanon during the Lebanese Civil War).
The movie contains a series of flashbacks to the mother's life (Nawal Marwan). Nawal, a Middle-Eastern Christian is impregnated by a refugee (likely a Palestine refugee in Lebanon). Nawal's infuriated brothers kill her lover as he and Nawal try to escape. She reveals to her grandmother that she is pregnant. They keep the pregnancy secret in order to save face. Upon the baby's birth, the grandmother tattoos the infant's heel, and they give the baby boy away. Nawal follows her promise to her grandmother to study in Daresh (a fictional city) during which a civil war breaks out. Under threat of war, Nawal returns to find her lost son. War has preceded her arrival as she discovers her son's orphanage at Kfar Khout has been destroyed. She then pretends to be a Muslim to board a bus with other Muslims fleeing to get to the camp where her son has been moved.
On the way to the camp her bus is attacked by armed Christians. She and a Muslim woman and her daughter survive, only to have the bus covered in gas to be burnt. Nawal escapes by showing her cross. They would not spare the woman, so Nawal claims the other woman's daughter as her own. However, the daughter runs back to the bus and is shot.
Disillusioned, Nawal joins a radical organization. She is planted as a French tutor for a prominent Christian leader and assassinates him. She is sent to Kfar Ryat prison for 15 years, and as prisoner number 72, despite all efforts of her captors, she remains resolute and becomes known as "The Woman Who Sings". Before her release, her enraged captors call upon the torture specialist Abou Tareq to break her spirit and stop her singing. He rapes her repeatedly and she gives birth to twins in the jail. A nurse secretly saves the babies and returns them to Nawal after her release. Nawal emigrates to Canada with the twins.
Upon her death, Nawal leaves a will requesting that her children, Simon and Jeanne, find their father and lost brother. Simon refuses, but Jeanne continues on her own, following in her mother's footsteps. She finds her extended family. They refuse to speak to Jeanne because of the shame her mother brought on the family. She then finds the prison and learns from a former employee that her mother was tortured and gave birth in prison. He gives her the name of the nurse who assisted Nawal during childbirth.
Distraught, she calls Simon to join her. He arrives with their mother's former employer from Canada. They find the nurse and ask about the baby who was born in prison. The nurse reveals their mother gave birth to twins, Janaan and Sarwan whom she safeguarded.
A local notary identifies the name of their lost half-brother as Nihad of May. They trace the warlord who conducted the revenge attack on Kfar Khout and destroyed the orphanage. Simon learns that the warlord had spared the children and took them in and trained them to fight alongside them. Nihad becomes a sniper and searches for his mother. He becomes crazed with war but is refused the chance to become a martyr by the warlord. He returns to Daresh as a sniper and is eventually captured by the enemy. They turn him to their side and train him to be a prison torturer. He is sent to the Kfar Ryat prison where Simon's mother was held. The warlord reveals that Nihad adopts the name Abou Tareq.
Having discovered that their father is their half-brother, they find out that he too had moved to Canada. They find him, and deliver the letters from their motherone for the father and one for the son. We learn that after many years living in Canada, while swimming in a pool, Nawal had spotted a man with a tattooed heel. She approaches him and although he does not recognise her, she realises upon seeing his face that he was also her rapist in prison. She suffers a stroke from the shock and eventually dies, giving instructions to her employer, a notary, about the letters and instructions for her children. Their task fulfilled, the children are now allowed to leave an engraved headstone at her grave.
Her first son, Nihad, having read the letters, realises what he had done to his own mother, and visits her grave.