The story of Naachiyaar revolves around a strict, tough and intelligent police officer namer Naachiyaar. She is assigned to a special case, which has some connections with Kaathavarayan, a youngster hailing from a slum. Two teenagers Kaathu (GV Prakash), a fruit vendor and Arasi (Ivana), a housemaid meet and start liking each other. The film opens with a pregnant Arasi being nabbed by ACP Naachiyaar (Jyothika) and another team led by Feroz (Rockline Venkatesh) arresting Kaathu who is accused of raping a minor.