Under the guise of a photojournalist sympathetic towards Salafi jihadism, Talal Derki is allowed to enter a village controlled by the al-Nusra Front close to the front line of the Syrian Civil War, and stays with the Osama family. The family patriarch Abu Osama is a enthusiastic fanatic, openly praising the September 11 attacks and naming his children after the leaders of al-Qaeda and the Taliban. He works as a sniper and as a mine remover, and removes his children from school due to coeducation. The children, in particular the eldest son Osama, become increasingly prone to fighting and bullying.

During a mission, Abu’s left lower leg is blown off by a mine. Shortly afterwards, the children are sent to a terrorist training camp. The boys face harsh conditions, and quickly become homesick. After returning home, Abu’s treasured books are destroyed in an airstrike by the Russian Air Force, and he lives by selling components from disarmed mines to bombmakers. He remains committed to his belief that the war will lead to an apocalyptic Third World War between a revived Caliphateand the Christian world and bring on the victory of the Mahdi against the Antichrist.

At the camp, Osama advances along and is prepared for further military training, while his younger brother Ayman does not do well and wants to return to school. Abu takes the decisive step of teaching Osama how to shoot a gun. Before Osama leaves for a more intensive camp, he shares a riddle with Ayman. Osama undergoes three years of training and indoctrination, while Ayman returns to school.

As Osama’s brigade is driven to the front for the first time and as Talal leaves to return home to Berlin, he explains that Ayman and Osama continued down their separate paths into their teenage years, and reflects upon the deep devastation of Syria.