Plot
A young boy is watching a girl’s birthday party from outside. The man who is with the girl sees the boy and later beats him for going there. He is later seen sneaking into the house of the birthday girl with a knife.
In Dehradun, Johnny Khanna is an eccentric forensic expert. He goes to a crime scene where a wife is murdered and the husband claims to be in cardiac distress. He immediately finds evidence that the husband murdered his wife.
In Mussoorie, a young girl in a school uniform sees another girl singing in a church, whose birthday it is. The birthday girl gives the schoolgirl candy. The next day, SI Megha Sharma is called to a crime scene in the rain. The murder victim is the birthday girl, whose name is Jennifer.
At home, the school girl is Megha’s deceased sister’s daughter, Aanya Khanna, who lives with Megha and her mother ( Madhuri Bandiwdekar). Aanya shows Megha a newspaper article with Johnny, who is her paternal uncle. Megha is visible annoyed.
Megha’s superior officer tells her that they are bringing in forensic expert Johnny and hopes that the two of them can remain professional. Johnny comes to Megha’s house to see Aanya and tries to address Megha. Megha coldly tells him that she is a stickler for police procedure and he should try not to get in the way. A flashback shows that Johnny and Megha were in love and planned to marry. Johnny then goes to stay with his slightly depressed older brother, Abhay Khanna.
At the church, Megha reviews the CCTV footage and sees Aanya talking to Jennifer. She also sees someone luring Jennifer outside and deduces that she may have known her killer. Megha asks Aanya about Jennifer and she tells her aunt that she was just listening to her sing. Johnny uses his forensic expertise to follow Jennifer’s path outside and to the location where she hit her head. Megha remembers the CCTV footage and remembers that the person that lured Jennifer was the same height as her. She remembers seeing someone with Dwarfism in the CCTV footage. Constable Rawat identifies him as Charlie, a performer. They capture him for interrogation, but Johnny is able to prove his innocence using science.
Aanya is seeing psychiatrist Dr. Ranjana to overcome the trauma of losing her mother, Divya and her twin sister, Aadya. Aanya claims her father loved Aadya more. Now Aadya is gone and she is not allowed to see her father. Dr. Ranjana practised out of her house and takes care of her father figure and mentor. She tells Megha that he was in remission for cancer, but his cancer has returned. Dr. Ranjana tries to convince Megha to allow Aanya to see her father, but she refuses. Abhay requests Johnny talk to Megha about letting Aanya see her father. When Johnny tries to talk to Aanya about her dad, Megha and Johnny fight.
A flashback shows that 5 years ago, Abhay lost Aadya during a fair in Rishikesh. She was later found dead by Aanya, having suffered a fall and hit her head on a brick. In grief, Divya commits suicide. Megha blamed Abhay for the tragedies. She breaks up with Johnny and takes Aanya away from Abhay.
Aanya and her grandmother attend a birthday for Aditi birthday party. At the birthday party, she disappears. After analysing the crime scene, Johnny deduces that the killer is a 10-12 year old. When Megha’s superior officer struggles to accept such a young serial killer, Johnny shows past examples of child killers: Robert Thompson & Jon Venables, Mary Bell, and Amarjeet Sada.
Megha informs her superior of a witness who saw a child in the crime scene where Jennifer was murdered. They are able get a sketch and distribute it. Megha gets a call from a mental asylum claiming that the sketch is that of Rohan, an 8-year old who killed his father. He escaped 3 months ago and was 11 at the time. The city goes on lockdown with school being cancelled, along with birthday parties.
Aanya disappears from Dr. Ranjana’s house. When Megha appears, she finds Aanya playing on a see-saw with Rohan. They capture Rohan and find Aditi’s body nearby. With the “Birthday Killer” caught, the city is now relaxed.
However, Johnny doesn’t think Rohan is the killer because he is right handed and evidence shows the killer is left handed. Megha and Johnny fight about this, until Megha discovers another young girl has disappeared. Aanya is shown pushing a wagon with a dead Birthday Girl on it.
Megha asks Dr. Ranjana to talk to Rohan to extract information on the missing Birthday Girl Bindya Pandit. Rohan tells her that a young girl tells him what to do. The news shows a video of Aanya pushing Bindya’s dead body on a wagon. Megha tries to find Aanya, but she is missing. Her teacher informs her that Aanya has been skipping school. Megha is suspended and Johnny is dismissed. Megha is put under house arrest.
Johnny sneaks in and convinces her to help him prove Aanya’s innocence. He tells her that he found Bindya’s body and has determined that the killer is an adult that may have manipulated Rohan and Aanya. Evidence led him to a house, where he found Bindya’s DNA. They don’t think the killer will murder Aanya until 3 days later, which is her birthday.
After seeing a drawing of Aanya’s, Johnny and Megha go to a Villa where they find Abhay with Aanya. Aanya has been meeting her father for a year, behind Megha’s back. Abhay confesses that when he saw Aanya’s news footage, he panicked and brought her to the villa. He was afraid that the killer might be after Aanya. Since her birthday is coming up, he tells Megha that he doesn’t want to lose Aanya on her birthday, the way she lost Aadya on her birthday. This gives Megha a hunch. Aanya also tells her that she was following the instructions of a young girl. Megha agrees to let Aanya stay with Abhay for her protection.
Megha’s hunch is confirmed: similar cases of girls murdered on their birthdays were reported in Rishikesh 5 years ago. Johnny seeks assistance from his mentor, the country’s foremost forensic scientist, Dr. Solanki. Assessment of bite marks from Bindya’s body and a Rishikesh victim shows the same DNA, but different bite marks.
The Rishikesh victims had a common psychiatrist, Dr. Ramesh Gupta. A neighbour informs them that Dr. Gupta went into remission from cancer but he was not happy. Upon discovering Dr. Gupta’s cancer, his adopted son Shashi committed suicide by jumping in front a train. Since the other victims were also found on train tracks, Megha suspects that Dr. Gupta was replaying his sons death with the victims. Upon seeing Dr. Gupta’s picture, Megha realises that Dr. Gupta is none other than Dr. Ranjana’s mentor. Megha and Johnny rush back to Mussoorie thinking Dr. Ranjana and Aanya are in danger.
Aanya is having seizure, so Abhay calls Dr. Ranjana who rushes over. Advance DNA phenotyping shows the DNA is of Dr. Gupta’s son Shashi. A closer examination shows that Shashi and Dr. Ranjana are one in the same.
Dr. Gupta reveals that he adopted the disturbed Shashi, the boy shown at the beginning of the movie, when he was about 12. Shashi wants to be a child psychiatrist, but his father’s cancer diagnoses triggers Shashi who goes on a killing spree. He then fakes his death and becomes Dr. Ranjana.
When his father’s cancer returns, he again goes in a killing spree. Shashi’s father loved his sister but not him. So seeing these girls with their fathers when he is about to lose his triggers her to kill. He also believes his father will recover if he kills these girls, just as he did in Rishikesh.
Dr. Ranjana attacks Abhay and hypnotises Aanya using a little girls voice. Flashback reveals how she hypnotised all the previous victims, who were all under her care.
Aanya is taken to the same house that the girls were murdered. Johnny and Megha go to rescue Aanya. Johnny rescues Aanya while Megha faces off with Dr. Ranjana. Johnny is forced to shoot her to save Aanya and Megha.
Abhay is reunited with Aanya. Megha and Johnny are back together and seen relaxing on a beach. They both receive calls about a series of murders in Goa, excited that they will get a chance to work together again.
