Tharkappu wants to be a battle cry against state-sponsored killings in the form of police encounters and death sentences. And it tries to argue its case through the tale of Sakthivel, an encounter specialist, who kills a criminal who murdered 16 people and tries to pass it off as self-defence (tharkappu). But a human rights official sees through his bluff and catches him red-handed and reforms him by making him see that corrupt politicians and businessmen have a hand in all his operations so far. Sakthi and his fellow cops decide to surrender in court, but their superiors decide to take them out for their political masters. Meanwhile, two couples on the run become entangled in this encounter operation and now, their lives are also in danger.

The plot of Tharkappu has scope for a decent action thriller, but the writing is uneven and so, the film isn't able to generate the tension that this tale needs. Also, the characters that RP Ravi comes up with are quite generic. A hard-nosed cop, an idealistic officer, naive youngsters, corrupt officials... While the narrative involving Sakthi (Sakthi Vasu does his best, but this is a performance where we are often being shown that he is acting) is interesting — the initial scenes keep his identity dubious and we are not sure if he is a good guy or a bad one. But the two romantic tracks are silly and implausible (the actors, too, are not charming), and break the momentum of the film. They are also the reason why the film feels overlong. And once Samuthirakani enters the picture, the film becomes a lecture class as the actor, as he often does, delivers his lines as if he is delivering a sermon in church. Meanwhile, Sakthi keeps monologuing that it becomes hilarious after a point.