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 eight years ago. Police inspector Sarita Sarkar (Vidya Balan) has no clue about the case. But he continues to search for the person who caused it, despite being discouraged by people all around him and collects evidence one by one at a slow pace.

John's wife Nancy (Padmavathi Rao) is sick and uses a wheelchair. Despite personal problems, John is determined not to give up. John also regularly meets Father Martin Das (Nawazuddin Siddiqui), who was a 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 become a priest.

One day, eight years after that tragic incident, there is another kidnapping, that of a boy named Rony. Everything about it echoes 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, with John, start investigating the case.

Since the modus operandi was the same, Angela's case file is reopened. Manohar is then nabbed when on the instructions of the unknown kidnapper of Rony (John), he tried 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 has kidnapped his own grandson. 

In the meantime, John doggedly pieces together the identity of Angela's kidnapper from little bits of information that he collects through his own investigations. After confirming the identity of Angela's kidnapper, 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.

Father Martin finds out that John 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 and is found guilty of his past activities. Manohar confesses that he kidnapped Angela since he needed money for his daughter's open heart surgery.

It is revealed that Angela was not murdered — while being held captive, she escaped and accidentally fell from a height onto a moving car and died. The car was driven by Father Martin Das, who was injured in the accident.