"Capernaum" unfolds through a flashback structure, framed by Zain's lawsuit against his parents. The central mystery is understanding the two crimes that define his present: the one that landed him in prison, and the one he accuses his parents of—giving him life.
After Zain's beloved 11-year-old sister, Sahar, is forcibly married off to their landlord's son, Assad, Zain runs away. His life on the streets leads him to Rahil and her baby, Yonas. When Rahil is arrested, Zain is left to care for Yonas alone, a period that forms the heart of the film. His desperate attempts to feed and care for the baby are both heroic and tragic. Ultimately, believing he has no other option to save Yonas's life, he agrees to give the baby to a morally ambiguous forger named Aspro, in exchange for the promise of passage to Sweden.
Zain returns home to retrieve his own (non-existent) ID papers but discovers that his sister Sahar has died from a complicated pregnancy. This is the film's most devastating turn. Overcome with grief and rage, Zain grabs a knife, finds Assad, and stabs him. This is the crime for which he is serving a five-year sentence.
From prison, he sees his mother on a TV talk show, pregnant again and unremorseful. This prompts him to contact the show and announce his intention to sue his parents to prevent them from having more children they cannot care for. The lawsuit culminates in his parents' emotional, though not entirely repentant, testimony. The court's verdict is not shown, but Zain achieves two victories: his parents are forbidden from having more children until they can prove they can care for them, and Rahil is released from prison and reunited with Yonas. The film's final, poignant shot is of Zain getting his photograph taken for his first identification card. After a film of unrelenting hardship, the photographer tells him to smile, and for the first time, he offers a genuine, heart-wrenching smile to the camera, a symbol of his newfound existence in the eyes of the world.