John Biswas (Amitabh Bachchan) is a 70-year-old grandfather who visits the police station regularly. He is desperate to find the kidnapper and murderer of his granddaughter Angela, who died 8 years ago. However, police inspector Sarita Sarkar (Vidya Balan) has no clues about the case. But he continues to search for the person who caused it, despite being dissuaded by people all around him and collects evidence one by one at a small pace.
John's wife Nancy (Padmavathi Rao) is sick and bound to a wheel chair. Despite the personal problems, John is determined not to give up. John also regularly meets Father Martin Das (Nawazuddin Siddiqui), who was once police inspector and was handling the Angela kidnapping case. Father Martin Das tries his best in solving the case but the guilt of being unsuccessful compelled him to leave his job and get converted to a priest.
One day, 8 years after that tragic incident, there is another kidnapping, that of a young boy named Rony and everything about it echoes of similarity with the kidnapping of Angela. Further investigation reveals that the modus operandi for kidnapping Rony is the same as that of Angela. Inspector Sarita requests Father Martin for assistance in cracking the case. Martin supports partially by providing clues and Sarita, along with John, start investigating the case.
In the meanwhile, John doggedly pieces together the identity of Angela's kidnapper from little bits of information that he collects through his own investigations and after confirming the identity of the actual kidnapper of Angela, he creates a plan to kidnap Rony. John wanted to seek revenge and justice since Rony's grandfather Manohar (Sabyasachi Chakraborty) was the one who had kidnapped Angela. Since the modus operandi was the same, Angela's case file is re-opened. Manohar is then nabbed when, on the instructions of the unknown kidnapper of Rony (which is actually John), he tries to flee with the ransom at the railway station. He is arrested by Sarita who interrogates him in the lock-up but he refuses to confess that he had kidnapped his own grandson Rony. Father Martin finds out that John had kidnapped Rony and confronts him. John requests Martin to arrange a meeting with Manohar. During the meeting, John makes Manohar confess about the crime committed by him in front of the police. Manohar confesses about the crime committed and is found guilty of his past activities. Manohar confesses that he had kidnapped Angela since he needed money for his daughter's open heart surgery.
It is also revealed that Angela was not murdered but while being held captive, Angela escaped and accidentally fell from a height on to a moving car and died. The car was driven by Father Martin Das, who was also injured in the accident.
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