Plot
Keshav Rajpurohit is a former IIT student who currently works as a teacher in a JEE tuition center. He hates his job and reaches out through LinkedIn, but fails to find a proper job. He belongs to an orthodox family; his mother is a homemaker and his father is a part of the RSS. He had a romance with a colleague, Zara Lone, who is pursuing her Ph.D. in IIT. Zara is from a Kashmiri Muslim family and their love story ends due to their families, who fight over religious issues. While Zara moves on and eventually gets engaged to Raghu Venkatesh (Keshav's classmate), Keshav is finding it hard to do so. He often gets drunk and calls Zara afterward, begging her to come back to him, to which she never agrees. Saurabh, his close friend, bids Keshav to forget his past love and focus on his future.
On Zara's birthday, Keshav controls his urge to call Zara and wish her at midnight. He and Saurabh drink and fall asleep. Around 3 a.m., he gets text messages from Zara asking him why he didn't wish her this year. Zara goes on and tells him to meet her in her room immediately. Keshav complies and rushes to Zara's room to wish her in person.
As Keshav enters the room, he finds that the room is dark and utterly silent. At first, he sees Zara on her bed, believing her to be asleep. Upon coming closer, he notices there is no pulse and finger marks on her neck, therefore realising that she is, in fact, dead. He informs Saurabh, who suggests they flee from the scene. Much to Saurabh’s chagrin, Keshav becomes determined to find the killer. He informs the police, Raghu (who was apparently beaten up by some local goons and is admitted to a hospital in Hyderabad), and Zara's parents. The police arrests the watchman of the hostel, who was missing from the CCTV camera during the time Zara was killed. Although police close the case afterwards, Keshav continues his investigation. He digs deeper with the help of police Inspector Vikas Rana. He first suspects Prof. Saxena (Zara's Ph.D. guide), who tried to harass her, but he realises Prof. Saxena isn’t involved in her murder.
After seeking of new suspects in the murder case, he tries to find Sikander, Zara's stepbrother who happens to be part of a terrorist group in Kashmir. Keshav seeks help from Zara's father and checks her room for clues. He finds a locker with gunpowder, pregnancy kits, and selfies of Sikander with a gun along with Zara. Keshav and Saurabh goes through the clues one by one. They first try to meet Sikander and asks him about his group, Tehreek. Sikander gets afraid and threatens them with a gun and runs away. They try to reach him out through his mother in Kashmir. Sikander meets them again and tries to explain that he is not the murderer. But with the proper clues, Keshav gets convinced that Sikander killed his sister in the fear that Tehreek might be known to the army. The next day Sikander kills himself, telling that his existence would harm Tehreek and convinces everyone that he did not kill his sister. After the suicide of Sikander, Keshav realizes he made a mistake by doubting upon him.
He then finds out about the pregnancy kits Zara had in her safe and sees a picture of an army officer and Zara’s childhood friend, Captain Faiz Khan, in Kashmir with her via Instagram. After proper investigation, he finds out that the army officer has gifted Zara expensive jewellery and along with Saurabh and Inspector Rana, raid his house in Delhi. The three discover gold blocks, the same pregnancy kits in Zara’s locker in Faiz’s house and check his internet history, which has search histories related to abortion and divorce. This leads them to believe that Faiz made Zara pregnant and killed her in guilt. They arrange a dinner party to announce the victim and arrest him unknowingly by inviting everyone Zara knew, after the 100th day of her death. Just before Keshav announces the killer, he goes on a trip to Hyderabad, where he checks the airport CCTV, only to find a covered up man travelling to Delhi during the hours prior to Zara’s death. He realises that Raghu is the killer. After the ceremony, Keshav and Faiz apprehend Raghu. Eventually he gives in and confesses to have killed Zara, because he found out she had an affair with Faiz and was perhaps pregnant with his child; Faiz tells, however, that she wasn't. While they did have an affair, it ended because Zara didn't want Faiz to leave his wife and kids alone, and because Zara loved Raghu. Raghu reveals he also paid some goons to ‘injure’ him; under the pretext of being admitted to the hospital, Raghu escapes the hospital on Zara’s birthday, travels to Delhi with a fake ID and upon visiting the IIT campus, strangles her in her sleep. It is also Raghu who impersonated as Zara and sent the text messages to Keshav on Zara's birthday. Raghu is hence, arrested by Inspector Rana.
The novel ends with Keshav visiting Zara's grave, and Keshav and Saurabh opening a detective agency: "Z Detectives".
