Amu is the journey of Kajori Roy (Konkona Sen Sharma), a 21-year-old Indian American woman who has lived in the US since the age of 3. After graduating from UCLA Kaju goes to India to visit her relatives. There she meets Kabir (Ankur Khanna), a college student from an upper class family who is disdainful of Kaju’s wide-eyed wonder at discovering the "real India". Undeterred, Kaju visits the slums, crowded markets and roadside cafes of Delhi. In one slum she is struck by an odd feeling of déjŕ vu. Soon after she starts having nightmares. Kabir gets drawn into the mystery of why this is happening, particularly when he discovers that she is adopted.

Meanwhile Kaju’s adoptive mother – Keya Roy, a single parent and civil rights activist in LA, arrives unannounced in Delhi. She is shocked to discover that Kaju has been visiting the slums. Although Kaju mistakes her mother’s response to a typical Indian over-protectiveness, Keya’s fears are more deeply rooted.

Slowly Kaju starts piecing together what happened to her birth parents and mother and daughter clash as Kaju discovers she has been lied to her whole life. As Kaju and Kabir undertake this quest they both discover their families' involvement with the man-made tragedy of immense proportions which took place twenty years ago in the capital city of India: the massacre of thousands of Sikhs in 1984; after the assassination of Indira Gandhi, the Prime Minister of India. Kabir learns that his father was instrumental in organizing the riots, as well as guilty of failing to stop Kaju's father from being killed. Kabir confronts his father who tries to justify his actions. Keya finally tells Kaju the truth; her birth name is Amu Singh and her Sikh father and younger brother were killed in the riots while her mother hanged herself in a refugee camp.