Once Upon a Time, Cinema is a comedy/drama/fantasy film about Nasser-e-din Shah (Ezzatollah Entezami), the king of Iran in the 19th century, who censors films and is against cinema.
After seeing Golnaar (Fatemeh Motamed-Aria), the lead actress in the first speaking movie in Iran (Dokhtar-e Lor), he falls in love with her and decides to pursue cinema in order to find her.
Another important character is Mirza Ebrahim Khan (Mehdi Hashemi), the Cinematographer, who appears in different times and eras throughout the movie, trying to convince the king about the beauty of cinema.
Once Upon A Time Cinema pays homage to cinema in general and specifically to Iranian cinema. The film includes clips from famous Iranian films and incorporates them into the plot in a surrealistic manner.
The movie concludes with a cinema paradiso-esque ending, featuring a screening of well-known Iranian films up to the production date in 1991.