The movie starts with the desperate attempt of surgeon Dr. Neela (Sharmila Tagore) to save a patient, who she knew was not going to survive. She works under the guidance of Dr. Chandra (Ashok Kumar), who tells her that however hard doctors might try, sometimes a patient will not survive. The story drifts into a flashback. Neela meets Avinash (Rajesh Khanna) at medical college and after an initial misunderstanding, grows close to him. Avinash is a poor man who works while attending medical college. He is a skilled commercial artist too, and Neela finds out that most of the portraits he paints are of her. Though Avinash admires Neela very much, he never talks about love or marriage. Everyone thinks that it is because of his financial status, but it is later revealed that it is because he is suffering from terminal cancer.
Neela, due to financial troubles, starts working as a tutor where she meets her student's (Mahesh Kothare) elder brother, businessman Shekhar Kapoor (Feroz Khan). Shekhar falls in love with her. He meets her elder brother Kalidas (I. S. Johar) to ask for her hand in marriage. Kalidas instead directs him to Avinash saying that Neela would heed his counsel. Shekhar is puzzled but meets Avinash nevertheless, who warmly approves of him and recommends him to Neela. Neela is shocked to learn that Avinash has blood cancer and cannot marry her. After an intense scene where he persuades her to settle down with the "wealthy, healthy" Shekhar, she finally agrees to marry Shekhar. The couple are initially happy together, but Shekhar always feels that Neela does not love him as much as he loves her. Facing losses in business, he desires Neela's sympathy but does not reveal his troubles to her. His insecurity prompts him to make his younger brother Montu stalk Neela everywhere she goes, fuelling marital discord.
Moreover, Neela regularly visits her brother's house where Avinash was a frequent visitor. She also visits Avinash's place. Shekhar slowly grows suspicious of Neela and Avinash and asks his younger brother to spy on her. Later he finds a "love letter", which was once written by Avinash as he imitated Neela's handwriting just for fun. However, in a grave misunderstanding, Shekhar thinks that Neela has indeed written that love note to Avinash and becomes devastated. He wants to set her free from their marriage, and ends up dying by suicide. Police suspect that Neela killed him and arrest her for murder.
In a surprising twist during the trial, Shekhar's mother Mrs. Kapoor (Nadira), who was always hostile to her daughter-in-law, testifies in favour of her unblemished character. The court acquits Neela. Later it is revealed that Avinash left to get away from their marital lives not knowing that Shekhar had committed suicide. He comes back in the final stage of his disease and dies in Dr. Chandra's hospital. Heart-broken and devastated, Neela has lost the will to live, but Dr. Chandra consoles her and takes her under his wing to make her a great surgeon like him. The film ends with Neela sending her brother-in-law Montu (Mahesh Kothare) abroad for studies and dedicating her life to the medical profession.
