Costao is a action, crime thriller about Costao Fernandes (Nawazuddin Siddiqui), a humble, honest and straight forward customs officer who is deployed in Goa and is feared by the department as well as criminals who use the seashores for smuggling. For Costao duty comes before family and adopts extraordinary strategies to bring smuggling down in Goa. One fine day he gets a tip-off from a reliable source that one of the biggest smuggling consignments is going to land at a secret place in Goa. To crack the biggest smuggling consignment ever in Indian history he goes all out to nab the culprits but realizes that there's bigger names are behind the whole game and this time he is the target. What happens when he ends up killing a popular drug lord in self-defence?