The film opens with Kiriti playing violin in his house. A visit from Mr. Dibraaj Mehta, a wealthy Parsee businessman, shakes the detective world he inhabits: Mehta hints that a figure called “Kalo bhromor” is blackmailing him, though no monetary demand has ever come, leaving Kiriti to wonder about the motive and the method behind the threat.
Days earlier, the shadow of trouble thickens around Nirod, Mehta’s business partner, who dies from dengue, while his nephew goes missing. To address the growing unease and to introduce the next generation of their enterprise, Mehta hosts a party that will pull many threads together. At the house of Nirod, Kiriti encounters Farzaana, a striking woman with red hair, and this glimpse hints at a wider web of secrets. He then seeks out [Dr. Sanyal] to understand the cause of Nirod’s death and the strange string of events encircling the family’s business.
That evening, Kiriti attends the party with a clear purpose: he informs Mehta that he cannot take the case, accusing him of concealing facts. Mehta pledges to reveal everything, setting the stage for a night of disclosures and danger. At the celebration, Kiriti is introduced to Krishna, Dibraaj’s daughter; her singing moment underscores a gala that will soon fracture under the strain of crime. When Dibraaj receives a call, he departs briefly and is fatally stabbed, leaving Kiriti to find a box containing a black wasp—the ominous symbol of the case, a recurring clue that will haunt the investigation: the Kalo bhromor.
As the investigation unfolds, Kiriti presses Krishna for information about the company’s hidden wings and the people who aided its shady operations. He reveals that illegal activities lurk behind the respectable facade of the family business, and that Kalo bhromor may have aligned with those illicit interests. After a tense exchange, Professor Kalidas Sharma, a note of academia and danger in one, approaches Kiriti to share that he was planning to leave his post because his research paper has just been accepted abroad. Kiriti wants to press for more, but Kalidas promises to talk the next day. That night, Kiriti shadows Kalidas’s residence in disguise and spots a figure he dubs the moonlight killer—someone who murders Kalidas as the sightlines of the night blur into certainty. He attempts to seize the culprit, but is stabbed in the arm; he fires a shot at the assailant’s legs, yet the killer escapes.
The next day, Inspector Salil Sen arrives with a troubling theory: Kiriti may be the moonlight killer, given his mobile-tower location data. Krishna, worried for Kiriti, visits him, and the pair counsels a cautious approach as they prepare for medical checks with Dr. Sanyal. When returning home, Kiriti learns from Dinataran Chatterjee that Farzaana is implicated in the kidnapping of Subrata, Nirod’s nephew. Kiriti hands the doctor’s prescription to a handwriting expert, who detects signs of a criminal mind in the script. The deduction strengthens Kiriti’s resolve to untangle the conspiracy.
Kiriti tracks Farzaana, but a hostile driver blindsides him, and he falls unconscious. He awakens, fights free, and shoots the goons, managing to rescue Subrata. A crucial clue surfaces: a letter signed by “kalo bhromor” that turns out to be written in the same handwriting as the doctor’s prescription. With the police, he storms Dr. Sanyal’s house to arrest the doctor, but Sanyal escapes, releasing a poisonous gas that puts everyone to sleep.
The following morning, Kiriti rushes to the police station after a call from Dr. Sanyal, only to learn that Krishna has gone missing. Dr. Sanyal sends a cryptic trail of clues and orders Kiriti to rescue her within 24 hours. Kiriti revisits Sanyal’s hospital and home and grows certain that the kalo bhromor and the moonlight killer are the same person. He deciphers the doctor’s riddle and heads to Barrackpore to close the net.
Meanwhile, Krishna makes a dangerous attempt to break free, but Sanyal succeeds in a chilling plan: the father betrays his three friends, and two are already punished by death. He intends to kill the third, using an injection to render Krishna unconscious, then plants a bomb and escapes. Kiriti wins a narrow victory by rescuing her, and the chase broadens to encompass the truth behind the symbol that haunts them all.
A startling realization reveals that the MLA is the third target, and Sanyal has relocated to Bolpur. Kiriti moves fast to warn him, while Subrata and Kiriti receive a notice that the doctor played a double game, bringing them perilously close to their targets. Kiriti arrives at the MLA’s room only to find the man dead; a chase ensues, and the doctor is shot, plunging into the river.
Krishna hurries to the nursing home where Kiriti is recovering, and asks what would happen if she takes responsibility for their future. Kiriti’s answer is measured, and Inspector Basu later reveals that Dr. Sanyal’s body cannot be found, fueling rumors and questions about who really survived the night.
Years pass, and Kiriti and Krishna share a peaceful, contented life. A jewelry surprise for their anniversary lights up the story’s warmth, but a newspaper headline shocks Kiriti into action: he travels to an abandoned church, where a surprising reunion awaits. Dr. Sanyal appears, revealed as someone who sought sanctuary with an orphanage after a past that bound him to violence—but who ultimately sacrificed himself when terrorists threaten the children. The church’s father and the orphans declare their loyalty to him, creating a powerful, conflicting tableau.
The final truth emerges in a quiet moment of reflection: the “kalo bhromor” is not a person but a symbol—a symbol of crime that lingers in the world. Subrata echoes the sentiment as Kiriti and Krishna’s life continues, shaped by the mystery they survived and the idea that some shadows never fully disappear.
