Sarah Ouseph is suffering from hallucinations probably related to her earlier career as an obstetric head nurse. She's living with her son, Bibin Ouseph, in Mundakkayam after retirement. Sarah is very controlling and Bibin is apparently okay with that. He works as a lab technician nearby and caters to all the needs of Sarah.
On a fateful day, Sarah reveals disturbing secrets related to her past to Bibin, and struggling to deal with how Sarah changed his destiny, Bibin attacks her and flees with Sarah's diaries. Sarah is admitted to a hospital and requests the doctor to arrange a meeting with a local CI and a legal advisor. She hands over 2 letters to them, one for the police and one for the magistrate. Soon after, Sarah dies while the police decide not to pursue the crimes done by Sarah as there is no way to deal with the social situation if her secrets are out in public.
However, the truth overwhelms Bibin and he chooses to go and learn more about his biological parents. As soon as he learns the one who was swapped with him is treating his parents poorly, he decides to make her go away and deviously concocts a plan that leads to her death.
Possessing information of the babies his foster mother swapped, he goes through one by one with the help of like-minded people who share his ideology, with the intention of eliminating individuals from the face of the Earth, especially those who did not live up to the opportunities they were given. However, he also starts sending a series of cryptic letters to a friend, which catches the attention of the Kerala police, and they are on his trail, led by Inspector Aji Kurien.
