Professor Mohan (Sunil Dutt) is a morally upright, honest young man living with his beloved mother (Leela Chitnis), who is single-minded in her pursuit of one goal: her son's marriage. Mohan teaches literature and poetry at a nearby college. During one lesson from a play composed by the medieval play-write, Shudraka about a nobleman who has fallen for a prostitute, he makes his abhorrent feelings about dancing girls quite clear.
Not long after, his mother, who is running a fever, falls down the stairs in their home and is unconscious. The doctor is called, injections are given, the neighbors all come crowding in, and much shaking of the head ensues, but she finally regains her senses long enough to say this, that she wants him to get married. The doctor pronounces his judgment that with the medication, she will get better; but the packed-in neighbors are much more gloomy. They all file out, still muttering amongst themselves.
One of the neighbors, Jeevan (Radhakrishan), has creditors hounding him, and he sees a little opportunity to make some money. He tells Mohan that he knows a girl who might be persuaded to pose as his fiancee for a few days, but her father will probably want money. Mohan, of course, is willing at this point to do anything and agrees to give Jeevan whatever he wants. Jeevan goes to see Champabai (Vyjayanthimala), a local prostitute. He negotiates a price with her for posing as Mohan's fiancee for the evening. Reluctantly, she puts on an ordinary sari and he takes her to see his mother and meet Mohan. Champbai, who was introduced as 'Rajni' by Jeevan before his mother puts up a credible demure act so as to impress her.
Champa, for her part, is unimpressed by either mother or son and makes fun of them when she returns to the Kotha. Jeevan gives her the agreed amount, which is promptly pocketed by the brothel owner, Lallubhai (Manmohan Krishna).
The next day, Mohan's mom asks to see Rajni Vyjayanthimala) again, and Mohan asks Jeevan to bring her again that evening. Jeevan has told Mohan that she is the daughter of a distant relative. In any case, Champa / Rajni is bowled over by the expensive jewelry that Mohan's mom shows her as the family bride-to-be. She decides to forgo her fee, to Jeevan's dismay, in favor of pretending to have real feelings for Mohan until she can find an opportunity to steal it. She soon does, as one day Mohan's mom gives her the bridal sari and jewelry to take home and try on and present herself as a bride before her.
She puts on the bridal outfit and comes before her customers that evening, but they make fun of her and ask her to perform as a bride/devi. She flees in humiliation and the jewels she put on so happily moments before now feel like they are scalding her. Her customers sing a lively qawwali to try and coax her out. But when she emerges, this time in her usual dance attire, they laugh at her again and she realizes that she means nothing to them, they don't think of her as a person with feelings or emotions. But, there is a life changing transformation in her when she realizes the respect and love a bride commands in a household. The next day, subdued, she brings back the jewelry and bridal sari to Mohan's mom, who is recovering nicely. Her warm greeting and kind affection make her feel even worse. Subconsciously, both Mohan and 'Rajni' had fallen for each other.
Meanwhile, Mohan wants to speak to her father. Jeevan puts him off, and he returns home to find Rajni there. He expresses his affection gently, and she tells him that she is not worthy of his feelings. She leaves sad, and the next evening refuses to dance for her customers. Lallu's threats don't move her either, and she throws him out after an impassioned speech about how he has been living off her earnings for years. He goes but vows that he will make her dance in the bazaar.
She goes to see Jeevan and makes him promise that he won't tell Mohan the truth about her, not because she thinks she has a future with him, but because she can't bear to become a fallen woman in his eyes. Soon after that, Mohan sees Rajni walking in the street. When he calls her name, she flees, and he follows her to the 'Kotha'. Mohan is horrified and angry when the people of the bazaar tell him that she is Champabai, a prostitute and not Rajni. He tells his bewildered mother that he will never see Rajni again.
Champa later writes a letter to Mohan that she wants to see him one last time at midnight outside his house. Mohan tears up the letter but still goes outside to find Champa standing there. He asks her why she wanted to see him and tells her to go away. She tells him that she is Champa and she is very sorry for cheating on both him and his mother. He immediately tells her that her profession is to cheat and betray people as she is a prostitute. She tells him that she was forced to become one but he doesn't pay heed to her. She leaves but gets kidnapped by Lallu and his cohort. But, hearing her cries Mohan saves her in the nick of time. He takes her back to his house and helps her regain consciousness. He asks her who they were and why they were kidnapping her. She tells him that they were MEN and they don't ask for consent on any matter. She then tells him how she was forced to become a prostitute after she was left alone in the world after her mother died suffering without any medicines. After hearing her story, Mohan tells her that he will marry her as Champa and not as Rajni. She becomes very delighted to hear this but tells him to go home immediately as she didn't want his mother to get humiliated knowing that her son goes to a prostitute's house.
Meanwhile, Lallu tells Mohan's mother that Rajni is actually Champabai, a prostitute. Shellshocked, she tells him to get out of her house and asks Mohan whether what Lallu said was true. Mohan's affirmation moves the ground under her feet and makes her very angry. At that time, Champa arrives at Mohan's house to take the blessings of Mohan's mother one last time before she leaves them for good, but she rudely asks her to leave. Lallu tells her that no gentleman would accept her but her customers will gleefully accept her back. Realizing this, Champa tells Lallu with tears in her eyes that she neither will be accepted by anyone nor does she deserve any other place than the bazaar. She turns to go out of the house when something irrevocably changes in Mohan's mother, who holds her back and tells her that she no longer is a prostitute after entering a household, which is like the flowing Ganges and she will not let her daughter-in-law go anywhere. Champa is overwhelmed and breaks down with tears of gratitude. The film ends on a happy note with Champa and Mohan reuniting.
