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.
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.
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.
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.