Rahasyam Parama Rahasyam (1988)

Gowri and Rajan are siblings devoted to each other. Rajan had to go to Dubai for six months to handle his business interests there, but dies in an unfortunate accident. A heartbroken Gowri performs the last rites of her brother, but is shocked when someone who claims to be Rajan arrives at her house. This apparent impostor has the dead Rajan's personal preferences and mannerisms, knows everything that only the dead Rajan knows and is even able to convince the Rajan's fiancee, Deepa about his identity. But Gowri is adamant that he is not her brother, and even has a victory in a court when X-ray images of the original Rajan does not match that of the newcomer. Yet, things are not the way they seem, and the real mastermind of the plot is someone else altogether.