Shekhar & Jayavrat are in Bihar for a blackmail scandal involving a famous politician. Shekhar is fascinated by the enigmatic Iraboty, while Mrinmoy discovers a classified file on "M," adding a new layer of intrigue to their investigation.

Iraboty's arrival in Lonpur sparks intrigue as she convinces Shekhar to investigate the 150-year-old Skhondokhata legend in Purulia, linked to recent deaths in the Bhaskar family. Shekhar suspects a deeper conspiracy.

Mrs. H & Pintoo are held hostage at Khasha Blanca forcing Shekhar to confront his past where he had uncovered a deadly gas weapon linked to M, a criminal mastermind. Now they must find the vial or his friends lose their lives.

Racing against time, Shekhar and Jayavrat hunt for clues across Calcutta left by the scientist Gupta, aiming to find a vial with the secret gas formula. As they near the final code, Shekhar faces M in a deadly struggle.