Sajarur Kanta is about a series of mysterious murders where the quill of a porcupine pierces the heart of the victim, killing him or her instantly. One victim does not die and Byomkesh is summoned. Konkona Sen Sharma plays Deepa, who belongs to a theatre group. She gets married to Debasish but makes it clear that she will not share conjugal relations with him. The two stories, one of Deepa and Debasish's married life and the other of the murder mysteries run parallel till they both converge.

A scientist accidentally finds a drug that can reveal an individual's past. However, when a few politicians fear their exposure, they plot to kill him.