The story of “Nizhal” revolves around an incident where Janani brutally attacks Vijay Hari, the son of industrialist Sivan Srinivasan, and two of his friends, leaving them hospitalised. Shocked by the attack on her son, Vijay Hari’s mother requests a police officer to investigate the case. As the investigation progresses, several shocking truths connected to Janani’s past life come to light, along with the revelation of a deeper criminal conspiracy behind the incident.