Inspector-General Sivaraj (Major Sundarrajan) appoints his son and fellow police officer, the talented and steadfast DSP Saravanan (Sivaji Ganesan) in charge of tracking down a virulent, anti-national smuggling ring. Saravanan is a widower with two kids who are being raised by his sister Ganga (Sumithra). When Saravanan gets some firm clues that a reputed local businessman and philanthropist 'Lion' Dayanidhi (M. N. Nambiar) could be the king-pin behind the cartel, Dayanidhi has him killed. Soon after, a distraught Sivaraj is introduced by a friend to a ferocious criminal lodged in Vellore prison named Sangili ((Sivaji Ganesan's dual role) who remarkably resembles his son Saravanan in appearance. Sivaraj decides to reform and train the brutish Sangili to impersonate Saravanan in order to trace those behind Saravanan's death.