Primarily set in the backdrop of the Kurnool village area in Andhra Pradesh, 'Siruthai' is liberally spiced with all the elements of commercial cinema. It is a double-action crime thriller that primarily revolves around two characters who just happened to look identical, Rocket Raja, a small-time thief, and Ratnavel Pandian, a brilliant police officer.
Rocket Raja (Karthi) is a small time thief who is talented enough to steal anything he comes across. In the company of Kaatupoochi (Santhanam), he enjoys life to its extent and even falls for the charm of a beautiful girl (Tamannaah). However, his life changes forever when a small girl comes to Raja claiming him to be her father.
As Raja finds out the girl's past, a flashback reveals that she is the daughter of an honest cop Rathanavel Pandian (Karthi), who is a nightmare to criminals and miscreants. However, Pandian is now is on the run because his enemies are behind him and his daughter. Eventually, the villains glean his whereabouts and murder him.
Hence, Pandian's colleagues who are desperate to find a solution, bring Pandian's daughter into Rocket Raja's life, in the hopes that he may take Pandian place. Initially reluctant, Rocket Raja eventually developed a special bond with Pandian's daughter and successfully completes the unfinished work of Pandian. He also takes care of his daughter. A roller-coaster ride of fun, joy, camaraderie and romance is what 'Siruthai' is eventually.