Sunday is a romantic thriller comedy movie that revolves around Sehar (Ayesha Takia), a voiceover artist who is an amnesiac and thus, hates to socialize. However, Ritu (Anjana Sukhani), Sehar’s best friend, takes her to a nightclub. She wakes up in her apartment, unaware of anything. She realizes that she has a recollection of the Sunday. Problems arise when she realizes that something sinister must have happened on the day, she recalls nothing about. She is helped by ACP Rajveer Randhawa (Ajay Devgn) to find out what might have happened with Sehar on Sunday. Will the duo find out the truth about the missing day?