Sarath Kumar's Sandamarutham is an age old story of an honest cop and his mission against a deadly villain, the only silver lining here is that Sarath Kumar has played both the villain and hero. Sarveswaran (Sarath Kumar) is a deadly don in Kumbakonam and he runs the underworld chemical bomb business to devastate the entire country. Mean time, we are shown another Sarath Kumar (Suriya) who is an undercover cop and he gets to know the real side through his honest cop friend Thirumalai (Samuthira Kani) who was murdered by the same chemical bomb. On his mission Suriya also encounters RR (Radharavi) who is a close friend of Sarveshwaran. The rest of the story tells how Suriya knocks down Sandamarutham.