That they know no evil will suspect none. So was the case with well known stage artiste Kishore. During his brief stay in Calcutta, he accepted an attractive present from toy merchant Dinu. Happy-go-lucky Kishore did not suspect any foul-play, but Dinu had concealed two pieces of a map in these toys. Dinu's only aim behind this was to send these pieces safely to Bombay, because another powerful gang headed by Rai Bahadur Dinanath was after this valuable map. Rai Bahadur who gets the information about Dinu's plan, follows Kishore to Grand Hotel. Here Rai Bahadur tries to strike a bargain with him. Kishore, who is ignorant about the whole affair, does not give any clear replies. In the mean while as arranged earlier Sitaram, a henchman of Dinu, manages to steal one part of themap from Kishore's room.
Disappointed in his deal with Kishore, Rai Bahadur offers him a seat in his private plane. During the flight he searches Kishore's luggage and gets another piece of the map and hurriedly conceals it in his cigarette case.
Rai Bahadur and Sitaram both realise ater that one part of the map was useless without the other. Both try to ransack Kishore's apartment, but unfortunately both of them run into each other. At the point if the gun, Rai Bahadur gets the address of Dinu from Sitaram. There is a scuffle between the two and Rai Bahadur kills Sitaram. But during this scuffle Rai Bahadur drops his cigarette case which while entering the room Kishore unconsciously stroves in his pocket. After a few seconds, Kishore notices a corpse in his almirah and screams. On hearing the scream other inmates of the hotel rush to the scene. Kishore is unable to give proper explanations. Hence people think that he has a hand in the murder but before anybody could catch him, Kishore escapes.
Next morning from Royal Hotel, Kishore telephones his sweet-heart Vimla. Vimla who has read the news of murder asks Kishore not so stir out of the hotel until she meets him. While discussing the whole story with Kishore, Vimla gets a clue that it is only the toy that can solve this mystery. So leaving Kishore in Royal Hotel, she goes in Kishore's apartment to get the toy. But to her surprise, she finds Rai Bahadur there. she overhears Rai Bahadur narrating the story to one of his gangsters that how he had dropped the cigarette case in the very same room and how valuable it was.
Now Vimla gets the clear picture of the whole mystery and in order to collect evidences against Rai Bahadur,she maneuvours to get a job as a maid servant in his house. But before she could break through the gang, Kishore who was hiding is caught by Rai Bahadur's gang and they secure the cigarette case from him.
While on the other side Vimla is also caught stealing the map red handed by Rai Bahadur. Having secured both the parts of the map and having known that it is unsafe to remain in city Rai Bahadur decides to escape in his plane with Vimla.
Could he succeed in his plans? Could Kishore prove his innocence?
Could Vimla escape from the clutches of Rai Bahadur? To know these answers you will have to see the thrilling climax of "Begunah".