Set in Bengal Presidency during 1881, the film shows a 5-year old Bulbbul getting married to few decades older Indranil who has a younger twin, Mahendra (who is mentally challenged), and the youngest Satya (who is closer to her age and whom she assumes is her husband). Twenty years later, we see Satya returning from London after studying law; Mahendra has died under mysterious circumstances and it has been five years since Indranil left home permanently. The young child bride, Bulbbul, is the thakurain of the ancestral mansion. Satya visits his elder widowed bhaabi who tells him some chudail killed her husband because she found reversed foot prints leading away from his body. More stories of men being killed in the village by a witch begin to capture the interest of Satya, enamored by the confident and self-assured Bulbbul who is shown to be an emotional wreck and docile when Satya was leaving for London.

In flashback throughout the movie, Bulbbul and Satya are always close being of the same age group. Mahendra is showing to be getting uncomfortably close to Bulbbul on many occasions and Indranil has to intervene. Sensing the bond between Bulbbul and Satya Indranil feels jealous and sends his brother away for education abroad. Bulbbul burns a diary which documents her co-writing a story with Satya, but Indranil finds a few corners which escaped the fire and misinterprets its content, loses his temper and beats her feet to a pulp. The doctor is called and told that she fell from the stairs and he skeptically informs Indranil that it may take a year for Bulbbul to even heal from her wounds in her feet. Indranil then leaves and says he will keep sending money to the family; there is nothing left for him there. Inside Bulbbul is still recovering from the pain and shock when Mahendra enters and rapes her, which results in her death. But suddenly she comes back to life, and you can see the change in her. Her sister in law comes and cleans away the evidence of her husbands rape and advises Bulbbul to keep quiet as she has married into a rich family and will keep getting silks and luxury, so she should not cry. The doctor enters and while putting her feet back into the slings notices blood and correctly assumes she was assaulted. However, the new bulbbul asks him to leave after his job.

At present she is informed on the anniversary of Mahendras death, that Satya's coach driver killed his first wife. While this is happening, Satya has gone to arrest the doctor who till now has become a confidant of the demon-bulbbul. Satya tells the doctor he will believe he is innocent if he sees the chudail himself. While on the way to the city, the driver is killed and Satya sees the chudail for the first time through the mist. He fires shots at her and vanishes into the fog. The doctor tries to go after him but finds Bulbbul on a tree in her full demoness glory, but she has been shot. He wants to help her but Satya stops him and sets fire to the nearby trees where she is hiding to kill her. The doctor tells him how she is not a demoness but a vigilante against men who commit crimes and calls her a avatar of Kali, the Hindu Goddess. He explains how she avenged pedophiles, abusive husbands, but never harmed anyone else. He even tells him that it is his sister in law - but in anger Satya does not listen. He finally realizes who she is when the doctor worriedly calls out for Badi Bahu - the title of Bulbbul in the manor, when he is looking for her in the flames. He then realizes what has happened and breaks down. Bulbbul is shown closing her eyes in the flames, giving the impression she is dead.

One year later, Indranil returns to a letter from Satya expressing how he never wants to be like his elder brother and is going away. While he is in the haveli, he hears a whisper calling him. Bulbbul appears, visibly scaring him and appears to be returning from the ashes and gives a sinister smile, implying she takes her revenge on him as well.