Gethu begins with Craig (Vikranth), a sniper, who is ordered to assassinate India's top scientist, Abdul Kamaal (if you did not get who the director is referencing here, here's another tip: he has written a book titled Agni Iragugal). The challenge for him is to draw Kamaal, who never gets out of his research facility, to make a public appearance. So, he comes to Kumily, a sleepy hill town, with a plan in mind. Meanwhile, in the town resides Sethu (Udhayanidhi), a librarian, and his father, Thulasi Raman (Sathyaraj), a PE teacher. The righteous Thulasi gets into trouble when he takes on Kandhan...