Robot

After a decade of research, the scientist Vaseegaran creates a sophisticated humanoid robot with the help of his assistants, Siva and Ravi, to commission it into the Indian Army. He introduces the robot, named Chitti, at a robotics conference in Chennai. Chitti helps Sana, Vaseegaran's medical student girlfriend, cheat in her examination, then saves her from being assaulted by a group of thugs. Vaseegaran's mentor, Professor Bohra, is secretly engaged in a project to create similar android robots for a German terrorist organization but has so far been unsuccessful. The terrorists give him a month to have the robots ready, otherwise, they will kill him.

Vaseegaran prepares Chitti for an evaluation by the Artificial Intelligence Research and Development (AIRD) Institute, which is headed by Bohra. During the evaluation, Chitti attempts to stab Vaseegaran at Bohra's command, which convinces the evaluation committee that the robot is a liability and cannot be used for military purposes. Vaseegaran's effort to prove Bohra wrong fails when he deploys Chitti to rescue people from a burning building. The robot saves most of them, including a girl named Selvi who was bathing at the time, but she is ashamed at being seen naked on camera and flees, only to be hit and killed by a truck. Vaseegaran asks for one month to modify Chitti's neural schema to enable it to understand human behavior and emotions, to which Bohra agrees. While nearing the deadline, Chitti becomes angry with Vaseegaran, demonstrating to him that it can manifest emotions.

Chitti uses Sana's textbooks to successfully help Sana's sister Latha give birth to a child. Bohra congratulates Vaseegaran on the achievement and allows Chitti to pass the AIRD evaluation. Chitti develops romantic feelings for Sana after she congratulates Chitti by kissing it. When Vaseegaran and Sana realize this, Sana explains to Chitti that they are only friends. Saddened by Sana's rejection, yet still, in love with her, Chitti deliberately fails an evaluation conducted by the Indian Army. Enraged, Vaseegaran chops Chitti into pieces, which are dumped by Siva and Ravi into a landfill site.

Bohra visits the site to retrieve Chitti, which has now reassembled itself, albeit in a damaged state. Bohra embeds a red chip inside Chitti while reconstructing it, converting it into version 2.0, which is more aggressive and unempathetic. It then gatecrashes Vaseegaran and Sana's wedding, kidnaps Sana, creates replicas of itself using Bohra's robots, and then kills Bohra after he attempts to kill Sana. Using its robot army, Chitti occupies AIRD and causes mayhem in the city. After informing Sana that it has acquired the human ability to reproduce, Chitti wishes to marry her so that a machine and a human being can give birth to a preprogrammed child, but Sana refuses. It eventually finds Vaseegaran, who entered AIRD to stop it, and nearly kills him before the police appear. The ensuing battle between Chitti's robot army and the police personnel leads to a lot of property destruction and many casualties. Vaseegaran eventually captures Chitti using a magnetic wall and accesses its internal control panel, whereby he instructs all the other robots to self-destruct. He then removes Chitti's red chip, calming it.

In a court hearing, Vaseegaran is sentenced to death for the casualties and damages caused by the robot army, but Chitti explains that it was Bohra who caused its deviant behavior and shows the court video footage of Bohra installing the red chip. The court releases Vaseegaran, while ordering that Chitti be dismantled. Left with no choice, Vaseegaran asks Chitti to dismantle itself. While saying goodbye, Chitti apologizes to Vaseegaran and Sana, who forgive it, before dismantling itself.

The film's setting then shifts to 2030. Chitti is now a museum exhibit. A curious school student on excursion asks her guide why it was dismantled, to which Chitti responds, "Naan sinthikka arambichen" (I started thinking).

AFTER 10 YEARS

Dr. Vaseegaran has recently built a new android humanoid assistant named Nila, whom he introduces to a group of college students. Shortly after, all the mobile phones in the city begin to fly into the sky, throwing the public into a panic. A scientific council assembles to discuss the phenomenon, in which Vaseegaran suggests reactivating the robot Chitti. But the plan is opposed by a member of the council, Dhinendra Bohra, whose father was killed by Chitti in the previous film.

The cell phones gather into a swarm and kill phone retail store owner Jayanth Kumar, telecom company owner Manoj Lula, and Telecom Minister Vaira Moorthy. The Home Minister S. Vijay Kumar gives permission for Vaseegaran to activate Chitti, whom he has already started working on. The cell phone swarm destroys phone towers around the city and wrecks havoc on the public, manifesting as a giant bird. A newly activated and upgraded Chitti battles the bird in the city and destroys it with an explosion. The remaining phones retreat and reform. Chitti, who runs out of battery takes refuge in three antennas at a space station. The bird tries to follow but is repelled by the antennas.

Chitti informs Vaseegaran about this incident and confirms that the phones are powered by an aura, specifically a concentrated mass of negative charge with electromagnetic properties. Since the space station was streaming positively charged ions into space, the bird was repelled. Vaseegaran builds a photon synthesizer that projects a positive charge, intending to neutralize the charge of the bird. The group confronts the bird and drains it of power. The phones take up a humanoid form, as the deceased ornithologist Pakshi Rajan.

Chitti converses with Pakshi as he attempts to destroy the synthesizer, in which a flashback reveals that Pakshi protested against the usage of modern mobile phones, from which the radiation affected the brains of birds and caused mass deaths. Pakshi makes conferences and protests to address this, but the public dismisses and mocks him. Lula and Moorthy also reject his morals for their business and Jayanth Kumar shun him from his shop as he tries to protest. Birds all over the city including Pakshi's sanctuary die out, including newborn chicks. A distraught and angered Pakshi, after even a court investigation found no violations (because telecom companies reduced signal levels to conceal wrongdoing), hangs himself at a cell tower. Pakshi's negative charged spirit reawakens by the radiation emitting from the tower. By absorbing the souls of all the deceased birds in the city, he becomes a vengeful entity.

Chitti tries to convince Pakshi not to hurt the public but Pakshi wishes to punish their ignorance. Chitti has Pakshi captured and contained. The news spreads to the council which decides to build an army of such robots for the military. Dhinendra, who becomes angered by Chitti's victory, releases Pakshi's spirit from the synthesizer. Pakshi possesses Vaseegaran and attacks the public again, but Chitti refuses to attack his creator. Nila gets the red chip and reprograms Chitti to his evil 2.0 alter ego, after altering it to not harm the innocent and commanding him only to fight Pakshi.

Pakshi traps 80,000 people in a football stadium and kills Dhinendra, who was present, by focusing radiation from multiple cell towers. Chitti interferes and fights Pakshi's bird form with his army. As Chitti runs out of charge, Pakshi turns into his winged form and creates several bird drones. The drones tear the robots into pieces, but before Pakshi can summon radiation he's interrupted by one of Chitti's creations: the action figure bot Kutti. Released into the stadium by Nila, the Kutti bots mount themselves on doves, forcing Pakshi to stand down. The Kuttis self destructs and destroys Pakshi's drones. After Vaseegaran is released from the possession, Pakshi is lead to the space station where he is destroyed.

Vaseegaran recovers in the hospital and tells Vijay Kumar, who comes to see him, that he feels Pakshi Rajan was a virtuous person who became a victim of the corrupt society. He also suggests that everyone should limit the use of phones, and conserve the lives of birds as much as possible. Chitti, now restored to its original version, begins a relationship with Nila.

In a post-credits scene, Sana asks Vaseegaran over the phone about the probability of mobile phones flying again. Immediately, Vaseegaran's mobile flies out of his hand and morphs into Kutti 3.0, saying, "I am your grandson".