This fast-paced crime drama revolves around Daya Shankar (Suresh Gopi), a fearless and forthright police officer, who lists a happy life with his mute young brother Nandu (Mani Kuttan) and his wife.
When a new menace and ethnicity in the form of Geevarghese alias GV, a powerful underworld don, who begins to encompass Kochi in a reign of crime and terror, Daya Shankar resolutely stands in his way.
After numerous confrontations, things get to such a point that GV harms Shankar's family, killing his Nandu (Mani Kuttan) and making his wife immobile. After this incident, GV offers his hand of friendship (hence the title Bada Dosth) and Daya Shankar accepts after resigning from the police force.
The story is narrated in flashback mode by the Bada Dosth (who has now become a Good Samaritan by starting orphanages, hospitals and homes for the destitute) to Commissioner Zakir Ali (Manoj K Jayan), who thinks the don still continues his illegal activities, proving that Daya Shankar's forgiveness was powerful enough to transform GV into Bada Dosth.