Osthe is the story of a daring stylish cop 'Osthe Velan' (Simbu). Simbu is a youngster living with his half-brother 'Jithan' Ramesh, his mother (Revathy) and his step father (Nasser). Simbu, with his subordinates (Santhanam, Thambi Ramaiah, Mayilsamy and Vaiyapuri), has a gala time in town. Then comes Sonu Sood, a corrupt man with a sole motive to win the by-election. He uses his power and influence and goes hammer and tongs to win the polls. Simbu becomes his nemesis. He plays spoilsport on all the plans of Sonu Sood. Ramesh is in love with Saranya Mohan but her father doesn't agree initially. Simbu gets attracted to Richa Gangopadhyay and they both marry. Revathy dies suddenly. After a chain of events Ramesh is caught by Sonu Sood. How Simbu rescues Ramesh from Sonu Sood's clutches is the rest of the narration.