The story begins with the cold-blooded murder of Mary John Kurishingal (Nafisa Ali). Her adopted sons arrive for her funeral from various places; Bilal John alias 'Big B' (Mammootty), Eddy (Manoj K Jayan), Murugan (Bala) and Bijo (Sumit Naval). The four brothers take it upon themselves to unearth the mystery behind their mother's murder. Bilal starts meeting his old friends and contacts in the Kochi underworld to get information on the killers. Little by little, they piece the evidence and find out that the murder was committed by two professional 'hitmen' from Mumbai. The ACP Balaji Shakthivel (Pasupathy) who is an upright cop, put in charge of investigations, tries his level best but cannot fetch any evidence to prove anything related. They soon find out that the murder was one of the many meticulously planned operations, aimed to check the teacher's intrusions into unlawful exporting of children from Kochi. As the Mayor (Ramesh Varma) and his henchman, an underworld don called Saiyuppu Tony (Sherveer Vakil) are involved, the brothers decide to take up arms to avenge their mother. How they accomplish their revenge forms the rest of the story.