Mumbai police inspector Sartaj Singh lives alone, having divorced his wife, and is disgusted by the corruption within the rest of the police force. He begins receiving calls from Ganesh Gaitonde, a wanted gangster who warns him that something destructive will happen in Mumbai within 25 days, and that everyone in the city will die except for someone named "Trivedi." Gaitonde recounts his life story to Sartaj over the calls, and claims to know Sartaj's late father, himself a policeman. Sartaj traces Gaitonde's location to a discreet safehouse, but Gaitonde shoots himself in the head when he is confronted.

News of Gaitonde's death creates a stir both in the public and within Mumbai police; Sartaj's senior officer, Parulkar, is contacted by film star Zoya Mirza as well as the Hindu nationalist home minister Bipin Bhosale, both of whom share a connection with Gaitonde. Parulkar suspends Sartaj from the case for not cooperating in an internal investigation into their unit, but RAW agent Anjali Mathur enlists his continued aid in uncovering Gaitonde's operation. The two of them learn that talent manager Jojo Mascarenas, a woman found murdered by Gaitonde at his hideout, is hiding fake currency from Pakistan and was procuring famous actresses as escorts for Gaitonde.

Anjali finds Mathu still alive at the site of a raid on his present-day operation. However, Mathu is soon assassinated in the hospital by assassin Malcolm Mourad. Sartaj uncovers evidence from Jojo's house showing that TV actress Nayanika Sehgal was an escort for Bunty Sharma, one of Gaitonde's most trusted gang enforcers. Anjali hatches a plan to use Nayanika as bait to lure Bunty out into the open, despite Sartaj's hesitance. Zoya is seen having dinner with Parulkar.

Nayanika is sent into Bunty's safe house with a hidden camera, but Bunty discovers it and holds Nayanika hostage. Sartaj is intent on saving her, but Anjali instructs him to follow Bunty's trucks instead. Sartaj traces Bunty to a warehouse where the latter tries to negotiate safe passage out of India with Malcolm. Sartaj is captured, but escapes the following morning with the help of his partner, Katekar, as well as Anjali. Bunty makes a deal with Anjali promising him passage out of India in exchange for all the information he has on Gaitonde. Nayanika calls Sartaj to rescue her from Bunty's hideout; Sartaj requests permission from Parulkar, who agrees to reinstate him if Sartaj supports a fabricated story exonerating Parulkar from an internal police brutality investigation.

Sartaj enlists the aid of the police force in helping rescue Nayanika from Bunty, but the operation is botched when Nayanika herself tries to murder Bunty and is accidentally killed by a police sniper. Bunty tries to escape, but is assassinated by Malcolm. Zoya's boyfriend blackmails her into starring in his father's film, knowing she was once an escort for Gaitonde. Sartaj begrudgingly gives a statement clearing Parulkar from the internal investigation despite knowing that Parulkar shot and killed an unarmed suspect in cold blood.

Sartaj visits his mother, who fails to provide an answer regarding his father's connection with Gaitonde. Meanwhile, Katekar finds a connection between a missing Muslim boy and a nearby theft after he is pressured to investigate the case, but one of the thieves murders him during an interrogation and escapes. Sartaj chases down the thief, who is unarmed, and shoots him dead. Zoya uses a self-inflicted injury to get her boyfriend arrested and thereby sabotage his blackmail attempt. Sartaj discovers Zoya's fake passports and her past as one of Gaitonde's escorts, while Anjali discovers a link between Gaitonde's former accountant and Malcolm Mourad.

Sartaj meets with Zoya and learns that she too was told by Gaitonde shortly before his death that "everyone will die except Trivedi." Sartaj and Anjali attempt to find Trivedi, and uncover an NGO owned by Bhosale that is being used as a front to smuggle unknown cargo through trucks carrying water tanks. Sartaj boards a train carrying the tanks to find its destination, while Anjali visits an address belonging to Trivedi. However, she is ambushed and killed by Malcolm.

Sartaj gets off the train at its destination, where he is immediately captured and brought to Malcolm, who cuts off his left thumb with an axe. Parulkar's forces soon surround the area; Malcolm escapes, but Sartaj discovers a large hangar full of crates carrying advanced weapons before collapsing from his injuries. He is hospitalized while the police interrogate an uncooperative Bhosale. Afterwards, Sartaj revisits his mother, who tells him that his father tended to Gaitonde while the latter was imprisoned. She plays a recorded video of one of Guruji's sermons where he recites the same philosophy Gaitonde told Sartaj over the phone, and Sartaj realizes the guru is Gaitonde's "third father." He returns to Gaitonde's hideout, where he discovers a nuclear shelter housing Trivedi's tortured body.

The police investigate Gaitonde's nuclear shelter and perform an autopsy on Trivedi's body. Sartaj and his fellow officer Majid Khan are recruited into a Special Investigations Team to monitor terror cells operating within Mumbai. Sartaj researches Guruji's ashram and learns that he died as recently as 2015. Malcolm sequesters Bhosale to a safehouse and interrogates Zoya to eliminate any more evidence that could link them to Gaitonde. Bhosale attempts to escape, but is caught and questioned regarding a possible nuclear attack in Mumbai. Sartaj and Majid investigate a local business printing pamphlets for Hizbuddin, an Islamic terror group led by the notorious Shahid Khan.

Sartaj visits Guruji's ashram, where he meets its director Batya Abelman and participates in one of her spiritual seminars. He and Majid learn from Anjali's diary that a group of Pakistanis stole nuclear fuel originating from Kenya. They connect the theft to the Hizbuddin pamphlets and are directed to a woman named Nasreen, who they find in a hospital suffering from radiation burns.

Sartaj and Majid learn that Nasreen accompanied two Pakistani twins, Malam and Alam, on a boat carrying an unidentified shipment to Mumbai. They track down the twins, who have also been burned by radiation, and learn of Shahid Khan's intentions to destroy the city. Additionally, Sartaj tracks down Katekar's troubled son Rohit, who has joined a street movement of Hindu nationalists. He confronts his guilt by revisiting Batya at the ashram, where the two of them take an herbal tea laced with a psychedelic substance. Sartaj later visits an aged Yadav at her daughter's home, where she is suffering from traumatic memory loss.

Sartaj's team learns that Malam and Alam where transporting lithium deuteride tubes to power a nuclear bomb. They investigate an online Hizbuddin chatroom in attempt to contact Shahid Khan. Outside of the investigation, Sartaj learns that his ex-wife Megha is pregnant with her new fiancée. Dejected, he visits Batya at the ashram once more, where they take a stronger dose of gochi and have sex.

The police's attempts to contact Shahid Khan backfire when Khan realizes the trap and kills the two men sent to deliver him the nuclear bomb. Sartaj begins suffering withdrawal symptoms from gochi; he unsuccessfully interrogates Bhosale and is later suspended from duty when the drug is found in his blood. Majid informs Sartaj that Parulkar cleared Khan's trucks for entry into Mumbai. That night, Sartaj encounters Malcolm on the streets and chases him down. Malcolm hints at a connection between Sartaj's father and the ashram before killing himself.

Sartaj confronts Batya about his father's connection with the ashram. Batya shows him proof that Dilbagh was a longtime member, and tells him about Guruji's plans of nuclear warfare in Mumbai. Sartaj reflects in solitude at a beach, but comes upon a street gang beating a Muslim boy for his religious beliefs. Sartaj spots Rohit in the crowd and attempts to break up the chaos, but the gang murders the boy and scatters. Disgusted, Sartaj returns to the ashram more convinced of their nihilistic ideology and takes another dose of gochi with Batya.

Parulkar realizes he was being used by Isa, his boss, to carry out Shahid Khan's plans. He attempts to confront Bhosale, who rebuffs him. Batya tasks Sartaj with recovering the Kaal Granth, a spiritual text authored by Guruji and stolen by Gaitonde. Sartaj breaks into the police's evidence room and recovers Gaitonde's biopic film, from which he learns that "Trivedi" is also the name of Gaitonde's father. He learns from Yadav that Gaitonde's father is still alive and visits him at his village, where the man has been keeping the Kaal Granth as a parting gift from Gaitonde. Sartaj brings the book to Batya's underground bunker, where she and other followers of the ashram are taking shelter from the impending attack.

Shahid Khan is shown to be Sartaj's cousin; his mother was separated from her sister (Sartaj's mother) during the 1947 partition between India and Pakistan. Majid's team brutally interrogates Khan's henchman for his location, while Bhosale confirms to the press that a nuclear attack will occur in Mumbai within 24 hours. A guilt-ridden Parulkar kills Bhosale before committing suicide. Sartaj experiences a vision of an apocalypse in Mumbai and decides to stop the attack, killing most of Guruji's followers in Batya's bunker before escaping. Khan activates the bomb in a parking garage as Majid's forces close in on him; Majid is killed in the ensuing shootout. Sartaj soon arrives with the Kaal Granth and uses it as a reference to find the pattern-based code to deactivate the bomb. The rest of the team evacuates the city while Sartaj makes a final attempt to stop the bomb; the screen cuts to black before the result is shown.