Pudhiya Paravai

Gopal (Sivaji Ganesan) is a rich businessman en route to India from Singapore on a cruise ship. He meets Latha (Saroja Devi), another traveller who has been accompanied by her father Ramadurai (V. K. Ramasamy). Gopal and Latha find that they like each other, so Gopal invites them to stay at his palatial mansion in Ooty, which they accept. One day, Latha discovers that Gopal gets agitated whenever he sees an onrushing train and demands the reason for it. Gopal explains that the reason behind this is his first wife.In a flashback, after losing his mother, Gopal, in his sorrow had been wandering aimlessly at Singapore. In a nightclub, he meets a singer named Chitra (Sowcar Janaki). He gets attracted to her and they decide to marry, in the presence of Chitra's brother Raju (S. V. Ramadoss). But he is disappointed from the very first day of their marriage, she comes home inebriated, and despite his repeated requests, has little respect for tradition and family values. Eventually, Gopal's father (Dada Mirasi) dies of a heart attack after seeing Chitra's drunken behaviour on Gopal's birthday. Gopal tries to control Chitra, but she is always irritated by his acts. At one point, she tries to leave him. Gopal begs her to change her decision, but Chitra still leaves. The next day, he hears that Chitra had died on a railway track, and this hurts him a lot. Latha sympathises with Gopal and accepts his love.Their engagement is fixed and while the reception is being held, a young woman walks in, claiming to be Chitra, accompanied by her uncle Rangan (M. R. Radha). Gopal says the woman is an impostor, but she and her uncle produce evidence which convinces even Gopal's police officer friend Kumar (O. A. K. Thevar). Chitra and Rangan become disruptive and Gopal gets frustrated, fearing that Latha might leave him because his "wife" has turned up. Several days later, Gopal reveals the truth to everyone. In a flashback, when Chitra was ready to leave Gopal, he slapped her. Chitra, suffering from a heart condition, is unable to take the insult of his slap and dies from the shock. Gopal realises that he had inadvertently killed his wife. To avoid arrest, and safeguard the honour of his family, he manipulates the murder to appear like a suicide on a railway track and fabricates the necessary evidence to show that Chitra committed suicide. Thus, Gopal escapes from the charges of murder. Not wishing to continue living in Singapore, he leaves by a ship to India.Upon hearing this, Latha and Ramadurai reveal themselves as police officers from Singapore investigating Chitra's death. Rangan is the local investigating officer, while the woman impersonating Chitra is actually Rangan's aide, Saroja. Together, they staged an entrapment in order to get the killer's confession, because there was no other conclusive evidence. Latha confesses to a dejected Gopal that though she initially pretended to love him, his good nature impressed her and she truly loves him; she promises that she will wait for him till he returns after completing his jail term. Gopal is relieved, but is still arrested and imprisoned.

Question: Who indavertently kills his wife?
Answer: Gopal