The sequel begins where Singam ended... Duraisingam (Suriya) is now on a top-secret operation to Tuticorin to dismantle an illegal weapon-smuggling ring.
On the personal front, Duraisingam befriends Susa (Santhanam) and Sathya (Hansika), the beautiful cousin of business tycoon Thangaraj (Rahman). For the sake of continuity, there is also a small flashback which reveals why his marriage with Kavya (Anushka) has been delayed.
As he embarks upon his mission his first obstacle comes in the form of Bhai (Mukesh Rishi), the local smuggler. With the help of Susa, Singam delves deeper into the criminal underworld only to discover that illegal weapons are just a cover for their real business, which is 'brown sugar trading'. He also unravels the key mastermind behind all these nefarious activities to be Danny (Danny Sapani), an international drug peddler who now wants to be the Kingpin of the Indian Ocean.
The war between the forces of good and evil heats up when Danny and Singam lock horns. With the help of a newly formed squad, Singam now decides to demolish the entire criminal network created by Danny, Bhai and their men.