A dangerous gang manufactures firearms and explosives, uses them for looting, derailing trains and disrupting law and order. They make bombs using sulphur from a match factory in Madras. A C.I.D. officer who is deputed to investigate these cases at Madras, finds several clues, reaches the factory and gets killed there. To investigate the case and to find who killed him, another CID officer Shankar is deputed by the DIG of Bombay. Shankar reaches Madras and from the time of landing, is followed by his enemies. Kumar at the Madras office assists him in the investigations.

Shankar faces several challenges and dangers and several attempts are made to kill him. He falls in love with Tara, sister of Sargunam, a doctor. Shankar's Madras office head unearths crucial information on the sulphur allotted for a match factory getting diverted to another place for making the explosives and firearms. But before he is able to report the complete information, he is murdered. Shankar's personal assistants Susi and Rajini are part of the gang and are instrumental in passing information about the investigations to the gang. They separately try to seduce Shankar, but fail.

Sargunam advises Tara to send Shankar out of Madras so that his life is not in danger. She drugs him to take him out of the city, then realises brother's intention is not to save Shankar, but to make him confess details of his investigations. However, Shankar, who was pretending to be drugged, wakes up and beats the people who try to get his confession; instead he makes them confess about their illegal activities. He learns that the gang leader Black Cat employs anti-socials and ex-convicts to make explosives and firearms, which he sells at phenomenal profit to anti-national and terrorist organisations.

With the help of Tara, Kumar and Kumar's girlfriend Ammukutty, Shankar reaches the match factory and follows the lorry which takes the sulphur to the factory where the bombs are made. He also finds Black Cat, revealed to be Sargunam. In the ensuing fight, Sargunam is killed and his factory torched, but Shankar, Tara, Kumar and Ammukutty escape unharmed.