After the death of her husband and her brother-in-law (devar), Gyatri Saxena, the widowed Rani of Devigadh, retires to a lonely deserted castle, accompanied by a faithful maid a devout servant. Rani spends most of her time in worship of the family diety (Kuldevta), and charitable acts to help the poor helpless villagers.
Suddenly one day a young man arrives in the castle proclaiming to be Ashok Saxena, the younger brother of the late Rai Bahadur Surendra Saxena, Rani's husband. Rani is baffled, because the pier of dead Ashok (her devar) was lit in her presence, in Manila, three years ago. Rani Gayatri Saxena rings up police inspector Girish Pandey of Devigadh and tells him to come and arrest the imposter. But the tricky youngman produces one evidence after another in his own favour to be Ashok Saxena. He even shows his own passport.
Rani too has enough evidence to prove that the youngman was an imposter, but strangely enough, all her evidence mysteriously disappears, at the nick of time. This encourages the imposter, who now insists that Rani is mad and that is why she does not recognise his identity. Confusion mounts to confounding heights.
DHUAN unfolds this mystery in most dramatic manner ever filmed.
(From the official press booklets)