Dhayalan "Dhaya" is a petty thief who has been arrested multiple times but never changes his ways. After being released from
Palayamkottai prison following his latest theft, he immediately steals a motorcycle and breaks into a house in
Kanyakumari. Inside, he finds an old man, Velayudham Pillai "Velan", chained to a window. To Dhaya’s surprise, Velan is not alarmed but warmly calls him “Kumar.” Confused, Dhaya warns him to stay quiet while he searches for valuables. Realizing Dhaya is not Kumar, Velan explains that he has
Alzheimer's disease and his son Kumar locks him up daily before leaving for work to prevent him from wandering off. Velan tells Dhaya there is nothing valuable in the house, but offers him ₹25,000 from his bank account if he releases him. Dhaya agrees, and they go to a nearby ATM. When Dhaya notices Velan’s account holds millions of rupees, he decides to exploit him further. Even after receiving the promised money, Dhaya stays with Velan under various pretexts. The two embark on a road trip to
Tiruvannamalai to meet Velan's brother-in-law MARKETING. Along the way, Velan’s memory lapses often cause him to mistake Dhaya for Kumar. Dhaya contacts his crime partner “Network” Ganesh, who lives in
Erode. Ganesh suggests that Dhaya photograph Velan’s ATM cards to duplicate them and obtain the PIN codes. Winning Velan’s trust proves difficult, as even Velan struggles to remember the codes. Dhaya begins to act like a friend, accompanying Velan to different places, and a bond slowly develops between them. Meanwhile, police investigate a murder in the house where Dhaya first encountered Velan. The crime appears linked to a serial killer who lures victims with phone calls and switches off the device after each murder. Authorities begin monitoring the phone’s activity. Later, Ganesh joins Dhaya and Velan at a party in
Salem. Velan spikes their drinks, rendering them unconscious. That same night, the serial killer’s phone reactivates, and the police trace it to Velan, who calls Siva Selvam, a corrupt schoolteacher, to demand a meeting. Velan confronts Siva about sexually exploiting his underage students and kills him. Before dying, Siva admits he has a partner named Arun and provides Velan with his number. By the time the police arrive, Siva is already dead, and no other clues are found. A flashback reveals that Velan’s wife Meenakshi was a child psychologist who counseled troubled children. During her work, she discovered that several girls had been abused but were too afraid to confide in their parents or the police. Meenakshi gathered evidence and filed a case, but her Alzheimer’s symptoms left her unable to testify coherently in court, leading to the case’s dismissal. Distraught, she commited suicide. Heartbroken, Velan vowed to avenge the victims, using her diary of abusers to track and kill them. It is also revealed that Velan does not have Alzheimer's or memory issues. He has been feigning memory loss, imitating his wife’s condition to cover his actions. In the present day, Velan and Dhaya visit Dhaya’s mother at his native village in Salem before leaving for
Palakkad to visit Velan's adopted daughter Krishnaveni. During their halt in
Coimbatore, Dhaya discovers a stash of SIM cards in Velan’s wallet, which makes him suspicious. Checking Velan's phone, Dhaya finds Velan's messages to Arun asking for underage girls. Unaware that this is Velan's plan to lure Arun out, Dhaya misunderstands the situation and assumes Velan himself is a
pedophile. He follows Velan after pretending to have fallen asleep, only to find Velan waiting for Arun at a location where they shared. No one shows up, and a disappointed Velan returns to his room. Dhaya witnesses everything and confides it to Ganesh. Dhaya and Ganesh plot to kill Velan at Ganesh’s farmhouse in
Coimbatore. They invite him under the pretence of a party. On the way, Velan realizes the car they are traveling in has the same hanging decor as was in “Arun's" contact profile picture. Velan remembers seeing the same model car the day before while waiting for Arun to show up. Putting two and two together, Velan realises Arun is Ganesh and confronts him at the farmhouse. A fight breaks out, and Ganesh easily overpowers Velan until Dhaya arrives. Having learned the truth, Dhaya sides with Velan, and together, they kill Ganesh. In the final reveal, it is shown that Dhaya delivered the fatal blow, but Velan takes the blame. The scene where Dhaya saw Velan the first time, in which Velan was chained to the window, also has nothing to do with Kumar or Alzheimer's. Velan was after his first target, a former jail warden turned pedophile, and got handcuffed by him in a struggle, but managed to kill him with the chain. When he saw Dhaya approaching, he started his ruse with Dhaya's help. == Cast ==