Ramprasad Dashrathprasad Sharma (Amol Palekar), a qualified CA, is looking for a job. He and his sister Ratna (Manju Singh) have no relatives or acquaintances except Dr. Kedar (David). Dr. Kedar tells him about Bhavani Shankar's (Utpal Dutt) firm known as Urmila Traders. Ramprasad is shown to possess many qualities. He is very good in accounting, is fond of sports and music, is a very good singer and also a very good actor (which he uses to get the job at Shankar's office).
Shankar is a man of traditional values: He hates youth wearing modern clothes. He is a sports fan, but thinks lowly of youth knowing anything about sports. But his weirdest trait is hatred towards men without mustaches. He thinks they are characterless.
Ramprasad has a mustache. He takes care of other problems by wearing a kurta and feigning ignorance about sports. Bhavani hires him immediately. Ram is a hardworking guy, so Bhavani (and Ram) have no problems. However, one day Ram takes leave by pretending that his mother (who died many years ago) has taken ill and goes to watch a hockey match. Bhavani Shankar, who attends the match, sees him there.
The next day Bhavani summons Ramprasad to his office and asks him about the hockey match. Remembering the plot of a movie a friend of his is shooting, Ram convinces Bhavani Shankar that he had seen his "mustache-less" identical twin Lucky (alias Lakshmanprasad Dashrathprasad Sharma) at the stadium.
Bhavani Shankar buys his argument and feels bad about accusing him. He makes amends by hiring Lucky to teach his daughter Urmila (Bindiya Goswami) music. Ramprasad reluctantly shaves his mustache to become Lucky and starts to teach Urmila. He is helped by his actor friend Deven Verma (playing himself).
Urmila (aka Urmi) is the exact opposite of her father. She takes an immediate liking to Lucky, while Ram is barely noticed by her. Bhavani notices this and gives Ram another job to tutor on the pretext of her exams. Meanwhile, Mrs. Srivastav (Dina Pathak), a socialite, is roped to play the part of Ram, "Lakshman" and Ratna's mother. Like Ram, she also ends up playing her own twin in front of Bhavani.
Ram tells Urmila the truth. Urmila tells him to tell the truth to Bhavani as well. Ram goes to Bhavani to tell the truth, but Bhavani sees Ram's mustache giving away. Bhavani exposes Ram but ends up thinking that Lucky murdered Ram and impersonated him to marry Urmila.
In a hilarious chase that follows, Bhavani ends up totaling a police jeep. The senior inspector (Om Prakash) mistakes him for a thug named Pascal D'Costa and is about to lock him up in the jail. Only when his inspector identifies Bhavani Shankar by his real identity is he freed. By now, a harried Bhavani has developed a hatred for twins as well.
On coming home, he finds that Urmila and Lucky are married. He refuses to give them blessings, until Dr. Kedar comes to the scene and explains the situation. Bhavani becomes even more furious but, on everybody's insistence, relents. The film ends with a family photo of Mrs. Srivastav, Ratna, Urmila, Ram, Dr. Kedar, Bhavani's sister Kalindi (Shubha Khote) and Bhavani (who is shown without a mustache).
(Synopsis credit: https://www.imdb.com/title/tt0079221/plotsummary/?ref_=tt_stry_pl#synopsis)