Dr. Chaudhary has to perform a surgery on an army officer shot by the police. However, he is in a dilemma because the officer has been sentenced to death.
The entire film production was completed in 28 days. Achanak was based on a Khwaja Ahmed Abbas story, The Thirteenth Victim, which had appeared in the magazine called Imprint. In 1973 N.C Sippy's sons, Romu and Raj Sippy collaborated with partner Hrishikesh Mukherjee to produce Achanak and they approached Gulzar to direct it. Gulzar approached Vasantrao, a marathi background score composer to compose the score for this film since it would have no songs otherwise.