In November 1942, shortly after the Japanese take over
Burma, a group of Chinese men from the
Green Gang are unloading
opium in
Calcutta. They are suddenly ambushed and their leader gets brutally blinded by a mysterious figure. Three months later, the leader decides to return to Calcutta to investigate their missing opium. Meanwhile, Ajit Kumar Banerjee takes help from
Byomkesh Bakshi to find his missing father Bhuvan Banerjee. Byomkesh initially rejects the request, but decides to investigate after his lover marries someone else. The following day, Byomkesh visits the lodging house Bhuvan resided in, headed by Dr. Anukul Guha, and takes a room to investigate. Byomkesh finds Bhuvan's
paan box with Ashwini Babu, Bhuvan's roommate, and deduces that he was murdered. Byomkesh visits the closed
chemical factory where Bhuvan used to work earlier and meets Anguri Devi, an actress and a close accomplice of the factory's owner Gajanan Sikdaar. Byomkesh finds some letters with Anguri Devi and deduces that Bhuvan was blackmailing Sikdaar, who might have killed Bhuvan and hid his body in the factory. Byomkesh and Dr. Guha return to the factory and find Bhuvan's body in a machine, causing
Deputy Commissioner Wilkie to question Sikdaar. However, Byomkesh discovers the letters are falsely backdated and saves Sikdaar from being framed. Byomkesh follows him home, but is stopped by Anguri Devi, who attempts to seduce him. Byomkesh meets Sikdaar, who immediately has a
fit and passes away, having been poisoned. Suspicion falls on Sukumar, who was seen making death threats to Sikdaar. Dr. Guha leaves Calcutta temporarily, but sends Byomkesh a stamp, confirming he had faked the letters and killed Bhuvan. Satyavati, Sukumar's sister, pleads with Byomkesh to help her brother, who she believes is innocent and in hiding. Byomkesh finds the cab Sukumar was last seen in, and the driver directs him to the office of Dr. Watanabe, a Japanese dentist. Byomkesh and Ajit meet Watanabe, saying that they are volunteers for Sukumar's
Basant Panchami agitation, but Watanabe suspects them and sends a real volunteer to follow them. Having observed this, Byomkesh and Ajit disguise themselves before following the volunteer back to Watanabe's office. Discovering the ruse, Watanabe kills the volunteer and his receptionist before escaping. The two enter his office and see their corpses, where Byomkesh finds a drawing in the volunteer's pocket. Returning to the lodge, Byomkesh and Ajit meet Dr. Guha, who admits that he and Sukumar are working with the Japanese to free the country, with Sukumar to lead a
Free Bengal, and killed Bhuvan and Sikdaar for betraying them. Returning to their room, Ajit vents about his father, revealing Bhuvan had lost his job at
Hind Chemicals when they learned his master formula contained opium and addicted customers. Realising Ashwini is addicted to Bhuvan's custom paan blend, Byomkesh takes a chew and
euphorically creates a mural of his understanding of the entire case, revealing Sikdaar said the words
Young Gun to him before dying. The next morning, Byomkesh tests the mixture and his own blood; while his blood contains
heroin, the paan is clean, making him deduce that Bhuvan had created an "untraceable" formula. Byomkesh learns from Kanai Dao, a fellow lodge resident and licensed opium dealer, that the opium supply in the local areas has been halted, and asks him if he can help Byomkesh meet any heroin suppliers. However, Kanai turns out to be a
police informer and turns Byomkesh and Ajit to Wilkie, who tells Byomkesh about Yang Guang, a former Green Gang leader who wanted Calcutta's opium business for himself, and was killed in retaliation, but reportedly survived; Byomkesh realises Sikdaar was referring to him about Yang Guang. Byomkesh discovers the drawing actually depicts the course of the
Ganges through Calcutta and Sukumar's campaign points. With Kanai's help, Byomkesh meets with the Green Gang, where they realise Yang had set a deal with the Japanese to use opium smuggling routes to invade Calcutta by surprise on Basant Panchami, in turn giving Yang control over the city's drug trade. Byomkesh realizes that Anguri Devi is Yang's lover, whom she has not met in 4 years, and she had killed Sikdaar and attempted to seduce Byomkesh on his orders while being unaware of Yang's deal with the Japanese. With the attack scheduled for the next day, Byomkesh meets Wilkie and requests him to set off all air raid sirens at 4 AM, but Wilkie refuses, and Kanai defects to Byomkesh for saving him from the Green Gang. Byomkesh requests Dr. Guha, Satyavati, Sukumar and Dr. Watanabe to meet him at the lodge, pretending to have joined them and claiming they have been betrayed. At the lodge, Byomkesh reveals Dr. Guha is Yang Guang, conned the idealistic Sukumar into his deal, and plans to make Calcutta as the drug capital of the world. Byomkesh states that he informed the authorities about the landing points, but Yang claims that he is bluffing. Anguri Devi attempts to dissuade Yang, nearly shooting him, but he shows affection to draw her in before stabbing her. The air raid sirens are set off; using this, Byomkesh convinces Watanabe to leave and stop the attack to save his men. The Green Gang, having secretly observed the proceedings with Kanai's help, attack Yang. Byomkesh informs a panicking Satyavati that he was indeed bluffing before being struck unconscious in the chaos. Byomkesh regains consciousness, where he is told by Ajit that the Green Gang has taken Yang. Byomkesh asks Satyavati to marry him, to which she smiles in reply. The Green Gang's leader orders his son to blind Yang in revenge at an abandoned factory, but Yang purposely blinds himself with the poker to turn the tables and kill the gang, where he plans the same for Byomkesh. As the factory siren rings, Byomkesh realises something is amiss. ==Cast==