Following the brief opening sequence of the mass killing of Kolkata Metro passengers by poison gas, the main narrative of the film begins when, two years after that terrorism incident, Vidya Venkatesan Bagchi (Vidya Balan), a heavily pregnant software engineer arrives in Kolkata from London, looking for her missing husband Arnab Bagchi. Vidya gets support from one junior police officer named Satyaki Sinha/Rana (Parambrata Chatterjee) in her quest to find out her missing husband who came in an assignment to work in the National Data Centre (NDC). Initial probes suggest that no man called Arnab Bagchi came to work in NDC, or stayed in the guesthouse that Arnab told about to Vidya during their telephonic conversations.
One human resource employee of NDC suggests Vidya that her husband resembled Milan Damji, an ex-employee of NDC. The HR employee is killed by Bob Biswas, an assassin (who works as a life insurance agent) before she could gather more data on Damji. Vidya, assisted by the friendly police officer Rana, breaks into the old office of NDC to collect paper documents on Damji. Here they have a close brush with the assassin who was also on the look-out for papers on Damji.
Meanwhile, attempted activities on Milan Damji's records rattle two high ranking Investigation Bureau (IB) officials — the chief Bhaskaran (Dhritiman Chatterjee) and his expletive spewing deputy Khan (Nawazuddin Siddiqui). Khan is sent to Kolkata, and it is eventually revealed that Damji was an IB agent gone rogue, who was responsible for the poison-gas attack in the Kolkata Metro. The IB has been looking for him ever since. Khan warns Vidya not to get deep into this matter, but Vidya is stubborn that she would find out her husband.
The residential address on Damji's records lead the investigating duo of Vidya and Rana to a dilapidated flat in one of Kolkata's narrow alleys. The errand boy of the neighbourhood tea-stall informs that the resident of that flat occasionally had a visitor. Paresh, a police-informer, provides them with some details about Milan Damji, and about an event two years ago when Damji got wounded. A doctor who apparently treated Damji gets assassinated, again by Bob, before he could supply any information.
The errand-by from the tea-stall identifies Sridhar, an IT officer of NDC, as the person visiting Namji's flat. Sridhar instructs Bob the assasin to kill Vidya. After a failed attempt to kill Vidya in crowded alleyways, Bob gets run over by a tempo during a running chase by Rana. Examination of Bob's mobile phone leads them to an IP address sending killing instructions. Vidya and Rana breaks into Sridhar's office to verify his IP address. Being alerted electronically, Sridhar returns to office, and pursues the duo. A commotion ensues, and Vidya shoots Sridhar accidentally. Khan, the IB official, is upset as they could not catch Sridhar alive.
Khan reveals that Rana has been all along working for him, and helping Vidya in her quest. Khan planned this as Vidya, a pregnant lady, would not generate much suspicion whereas police or investigation bureau—if they had done the investigation—would alert the culprits who supposedly have reach to the higher echelons of the investigation bureau itself. Although not happy at her being used as a ploy, Vidya agrees to help Khan. Further examination of Sridhar's computer reveals a code which is deciphered to be Bhaskaran (IB chief) phone number. Khan guesses that Bhaskaran himself may be the mole within IB. According to his plan, Vidya calls Bhaskaran, and tells him that Vidya has got hold of sensitive documents from Sridhar's office, if Bhaskaran helped Vidya to find out her husband, she wound hand over the documents to Bhaskaran. Bhaskaran nonchalantly tells Vidya to contact local police as he is not associated with this. However, within a few minutes of this conversation, Vidya gets a call from unknown number, warning Vidya that she should hand over the documents if she wanted to save her husband.
This unknown caller later calls Vidya again, introducing himself as Milan Damji. He tells Vidya to meet him in Triangular Park. Khan and Rana manage to find this out and reach the place as well, but fail to trace her in the crowd. They believe she is in danger as Damji will inevitably kill her because she knows his identity and fugitive status. In a dark alley, however, the two come face to face. Damji demands that she return whatever evidence she might have against him, and it becomes quite clear that neither is he her husband, and nor will he flinch from killing her. He strikes at her stomach, hoping to destroy her child. It is then revealed that Vidya is herself on a mission to kill Damji, and her pregnancy is fake. She strikes a momentarily perplexed Damji with her hairpin, killing him. Amidst the commotion of the Durga Puja immersion, Vidya disappears into the crowd. She leaves a thank you note to Rana. Rana, on the basis of some clues that are shown to the viewers (most of which were earlier shown in the proceedings of the film), deduces that there was no Arnab Bagchi at all, and Vidya all along has actually used police and investigation bureau to achieve her mission—to kill Damji.
It is then revealed that Vidya is the widow of Arup, an IB operative who was the officer shown in the beginning of the film who was trying to locate the bag containing the poisonous gas that killed multitudes in the Metro Rail incident. He dies in the event. Damji was a colleague of Apurba in IB, but he went rogue and cooperated with terrorists. In her mission, Vidya was helped by Colonel Vajpayee, a retired top IB officer, who suspected that some top IB official was associated with the Metro Rail killing.
TV news reports show arrest of Bhaskaran for being associated with the killing. Rana joins a candle-lit vigil for those who died in the Metro Rail killing. The film ends with a short background monologue by Amitabh Bachchan on the mythological and cultural significance of Durga, while on screen the the Durga idols are immersed in Ganges (the ritual of Bisrajana at the end of Durga Puja festivities).
Following the brief opening sequence of the mass killing of Kolkata Metro passengers by poison gas, the main narrative of the film begins when, two years after that terrorism incident, Vidya Venkatesan Bagchi (Vidya Balan), a heavily pregnant software engineer arrives in Kolkata from London, looking for her missing husband Arnab Bagchi. Vidya gets support from one junior police officer named Satyaki Sinha/Rana (Parambrata Chatterjee) in her quest to find out her missing husband who came in an assignment to work in the National Data Centre (NDC). Initial probes suggest that no man called Arnab Bagchi came to work in NDC, or stayed in the guesthouse that Arnab told about to Vidya during their telephonic conversations.
One human resource employee of NDC suggests Vidya that her husband resembled Milan Damji, an ex-employee of NDC. The HR employee is killed by Bob Biswas, an assassin (who works as a life insurance agent) before she could gather more data on Damji. Vidya, assisted by the friendly police officer Rana, breaks into the old office of NDC to collect paper documents on Damji. Here they have a close brush with the assassin who was also on the look-out for papers on Damji.
Meanwhile, attempted activities on Milan Damji's records rattle two high ranking Investigation Bureau (IB) officials — the chief Bhaskaran (Dhritiman Chatterjee) and his expletive spewing deputy Khan (Nawazuddin Siddiqui). Khan is sent to Kolkata, and it is eventually revealed that Damji was an IB agent gone rogue, who was responsible for the poison-gas attack in the Kolkata Metro. The IB has been looking for him ever since. Khan warns Vidya not to get deep into this matter, but Vidya is stubborn that she would find out her husband.
The residential address on Damji's records lead the investigating duo of Vidya and Rana to a dilapidated flat in one of Kolkata's narrow alleys. The errand boy of the neighbourhood tea-stall informs that the resident of that flat occasionally had a visitor. Paresh, a police-informer, provides them with some details about Milan Damji, and about an event two years ago when Damji got wounded. A doctor who apparently treated Damji gets assassinated, again by Bob, before he could supply any information.
The errand-by from the tea-stall identifies Sridhar, an IT officer of NDC, as the person visiting Namji's flat. Sridhar instructs Bob the assasin to kill Vidya. After a failed attempt to kill Vidya in crowded alleyways, Bob gets run over by a tempo during a running chase by Rana. Examination of Bob's mobile phone leads them to an IP address sending killing instructions. Vidya and Rana breaks into Sridhar's office to verify his IP address. Being alerted electronically, Sridhar returns to office, and pursues the duo. A commotion ensues, and Vidya shoots Sridhar accidentally. Khan, the IB official, is upset as they could not catch Sridhar alive.
Khan reveals that Rana has been all along working for him, and helping Vidya in her quest. Khan planned this as Vidya, a pregnant lady, would not generate much suspicion whereas police or investigation bureau—if they had done the investigation—would alert the culprits who supposedly have reach to the higher echelons of the investigation bureau itself. Although not happy at her being used as a ploy, Vidya agrees to help Khan. Further examination of Sridhar's computer reveals a code which is deciphered to be Bhaskaran (IB chief) phone number. Khan guesses that Bhaskaran himself may be the mole within IB. According to his plan, Vidya calls Bhaskaran, and tells him that Vidya has got hold of sensitive documents from Sridhar's office, if Bhaskaran helped Vidya to find out her husband, she wound hand over the documents to Bhaskaran. Bhaskaran nonchalantly tells Vidya to contact local police as he is not associated with this. However, within a few minutes of this conversation, Vidya gets a call from unknown number, warning Vidya that she should hand over the documents if she wanted to save her husband.
This unknown caller later calls Vidya again, introducing himself as Milan Damji. He tells Vidya to meet him in Triangular Park. Khan and Rana manage to find this out and reach the place as well, but fail to trace her in the crowd. They believe she is in danger as Damji will inevitably kill her because she knows his identity and fugitive status. In a dark alley, however, the two come face to face. Damji demands that she return whatever evidence she might have against him, and it becomes quite clear that neither is he her husband, and nor will he flinch from killing her. He strikes at her stomach, hoping to destroy her child. It is then revealed that Vidya is herself on a mission to kill Damji, and her pregnancy is fake. She strikes a momentarily perplexed Damji with her hairpin, killing him. Amidst the commotion of the Durga Puja immersion, Vidya disappears into the crowd. She leaves a thank you note to Rana. Rana, on the basis of some clues that are shown to the viewers (most of which were earlier shown in the proceedings of the film), deduces that there was no Arnab Bagchi at all, and Vidya all along has actually used police and investigation bureau to achieve her mission—to kill Damji.
It is then revealed that Vidya is the widow of Arup, an IB operative who was the officer shown in the beginning of the film who was trying to locate the bag containing the poisonous gas that killed multitudes in the Metro Rail incident. He dies in the event. Damji was a colleague of Apurba in IB, but he went rogue and cooperated with terrorists. In her mission, Vidya was helped by Colonel Vajpayee, a retired top IB officer, who suspected that some top IB official was associated with the Metro Rail killing.
TV news reports show arrest of Bhaskaran for being associated with the killing. Rana joins a candle-lit vigil for those who died in the Metro Rail killing. The film ends with a short background monologue by Amitabh Bachchan on the mythological and cultural significance of Durga, while on screen the the Durga idols are immersed in Ganges (the ritual of Bisrajana at the end of Durga Puja festivities).
