Kusthi movie revolves around Jeeva (Prabhu) runs away from home unwilling to marry local chieftain (Radha Ravi)’s daughter. He goes to his friend Vels’(Vadivelu) residence in Chennai. There he works with him in a Fast Food restaurant.
Singam (Karthik) makes his living as a gangster. He has his own mob and henchmen. But he is not a real gangster and only pretends to be one. One day one of his henchmen is caught by a real mafia group. Jeeva helps the henchman to get away from this tight corner situation and this leads to the bloom of friendship between Jeeva and Singam.
Abhi (Flora) misunderstands Jeeva’s activities and assumes him to be a blue-cross member. She falls in love with him. Meanwhile Singam falls in love with Dhivya (Manya). Abhi and Dhivya are sisters.