Once Upon a Time in Mumbaai is a romantic crime drama. The movie revolves around two gangsters, Sultan Mirza (Ajay Devgn) and Shoaib Khan (Emraan Hashmi). It is set in 1970s Bombay. Sultan Mirza, a kind-hearted smuggler becomes the king of Mumbai’s underworld. Meanwhile, Shoaib is an ambitious youngster who has a dark character and wishes to take over the Mumbai underworld and run the criminal world on his own terms. The movie narrates the story of the eventual downfall of Sultan Mirza that helped Shoaib to rise to power.