An accident (a bomb blast in Bombay) 16 years ago destroyed Nanda’s family – her parents and sister. Only one sister survived, and that was Radha, Nanda’s younger sister who was to be married soon. Radha lost her memory in the blast, so Subodh was easily able to persuade her that she was his wife, Nanda. Everybody else was told that Radha died in the blast. Radha’s fiance had met her only once (which is why he wasn't able to identify her 16 years later) and accepted her death, unquestioningly. Nalini, Subodh and Nanda’s daughter, must have been young enough to accept her Aunt as her Mom. Subodh and the new Nanda then made their home in Darjeeling (where I assume nobody knew the real Nanda). There, Radha was Nanda for 16 years before she had another bang on the head and returned to her present (of 16 years ago)!
Once Subodh realised that Radha couldn't be coerced into being Nanda, he set out to prove her insane, so she wouldn't be believed. Hence the “dead body” in her closet which was really a live woman who disappeared once she had scared Radha, but before anybody else arrived on the scene. Rajesh began his investigation into Radha’s story. From 16 year old hospital records he found that Nanda was the sister who died, and then everything fell into place. Subodh made one last attempt to retain his "wife" by running away with an unconscious Radha but a fortunate road accident on the way put paid to his existence. Radha and Rajesh lived happily-ever-after after that!
Shankar and Ranjana travel to faraway places where he hopes that he won't hear Kamini's haunting love song and finally be able to live happily-ever-after with his wife. But no matter how far they travel and what they do, he is still unable to forget Kamini. We find out about what happens on these travels through Ranjana's bitter letters to her Bhabhi. After two years of this madness, Ranjana decides to bring matters to a head and find out what ails her husband. She writes him a suicide note and disappears. Shankar is overjoyed to become a widower and rushes home to Kamini. Ranjana follows him and finds out that he loves another woman, and decides to avenge herself on both for her ruined life (but not before she's written to her Bhabhi about her plans, in detail). She swallows poison and then goes to the police to record her dying statement. She alleges that she's been poisoned by her husband so that he could be with his lover. She dies soon after and Shankar is arrested for her murder.
Shankar's lawyer friend Shrinath makes a valiant attempt to defend him. He has a surprise witness for defence: the Mahal's caretaker's veiled daughter Asha. When the veil is lifted, Asha is revealed as Kamini herself! She tells the court that growing up in the Mahal with the legend of Kamini and her faithful lover, she began to pretend that she was Kamini, too, and wished to be loved as wholeheartedly as the latter was. She used to walk around singing in the Mahal, pretending to be Kamini. After one such interlude, she saw Shankar and also witnessed how powerfully affected he was by the startling likeness between himself and Kamini's long-dead lover. Here was the opportunity for a servant girl to be loved truly and deeply by a man like Kamini's lover! So she played upon his feelings, using the Mahal's secret ways to good effect to convince him that she was Kamini's spirit. Once Shankar was hopelessly in love with her, she had planned for him to see Asha and realise that he could have his Kamini in her. Unfortunately, Shrinath interfered and Shankar landed up emotionally blackmailed into marrying Ranjana.
Unlike us, the trial court is less than impressed by Asha's story, and Shankar is sentenced to be hanged for murdering Ranjana. The day before his hanging, he requests Shrinath to marry Asha before he dies, so that he will permanently lose her in this lifetime, hopefully to be re-united with her in the next. As luck would have it, Ranjana's letter, detailing her revenge plan to her Bhabhi, is finally found by the police (I think it got lost in mail). Shankar is promptly released, and he makes his way to Shrinath's place. Shrinath and Asha have just been married, but when the former realises that his friend has been spared to live a long life, he declares his intention to make the supreme sacrifice. Before he can do so, though, Shankar drops dead. THE END.