The story of Being Cyrus revolves around a Parsi family - Sethnas, residing in the hills of Panchgani. A retired sculptor Dinshaw (Naseeruddin Shah) heads the family. He lives with his wife Katy (Dimple Kapadia).

Other members of the this family comprise of Dinshaw's brother Farokh (Boman Irani), sister-in-law Tina (Simone Singh) and second brother Fardoonjee (Honey Chhaya).

Cyrus (Saif Ali Khan) shows up at the Sethna house in Panchgani and offers to be an assistant to Dinshaw. He spends a year with them and in the process a romance seemingly brews between him and Katy. Other secret activities coincide with this; Cyrus receives some money for an undisclosed reason, and he is shown working on something in a lab setting.

He then arrives at Dinshaw's brother, Faroq's house in a very Parsi locality in Mumbai. Faroq takes care of their father who lives in a room in their Mumbai apartment, and does not treat him too well. Cyrus befriends the father but Faroq loathes his proximity.

Katy on the other hand, gets frequent calls from Mumbai, in a parallel unexpected development. Tina, Faroq's wife, befriends a policeman Lovely (Manoj Pahwa), their interactions provide good comic relief.

As the movie proceeds it gains a psychological insight into the family and reveals that everything is not all right with the Sethna family. Not just that, even Cyrus comes across as a bizarre personality. The plot slowly unfurls, revealing morbid and unanticipated sides of many. The movie takes a shocking turn at one juncture.

The story brings out the dark sides of some seemingly ordinary characters, who eventually go to unbelievable lengths to achieve their goals.

Being Cyrus is the directorial debut of Homi Adajania and Saif Ali Khan's first film in English.