NIZHAL follows twin sisters Ramya and Saranya. Saranya is a trainee doctor, and Ramya helps their vendor parents. Tragedy strikes when Saranya’s friend Lakshmi is brutally murdered in the hospital lab by Guna, the CEO's son, and his gang. Ramya witnesses the crime and narrowly survives a deadly attack by them. Driven by fury, Saranya seeks vengeance and puts the killers on their deathbeds. Ironically, her lover Raghu takes charge as the sub-inspector for this very case. When Raghu uncovers the truth, a gripping battle begins between law, love, and ultimate justice.