Velu (R. Sarathkumar) is living happily with his sister and friend Pazhani (Vadivelu) in Palani. He stays away from all wanted troubles and is forced to resort to fighting to defend his sister from the local rowdy Raghavan (Vincent Asokan). A flashback follows where it is revealed that Velu is a military officer and his sister is actually the sister of his best friend, Police Officer Murugan (Kalabhavan Mani) of Chennai. It is also revealed that Velu had maintained a low profile to protect his sister from his foe Naachiyar (Kota Srinivasa Rao) whom he had left crippled before he went into hiding.
Vasudev Shastri (Utkarsh Sharma) is a topper yet charming man who comes into IIT where the second ranker, Nandini (Ishitha Chauhan), decides to make his life hell. But Vasu is smart and in love with her to be outmaneuver. Besides being the friendly ‘genius’ around campus, he has also got a part-time job working with RAW (Research and Analysis Wing) where his hacking talents are occupied.Vasu was orphaned when his parents were killed in communal riots. He was found by a priest who raised him in a temple complex in Mathura. The life-positive Vasu is the one we see in flashback. In the present, Vasu dresses in all-black, uses a walking stick and suffers from acute tinnitus. This troubled, damaged Vasu is the one who survived multiple bullet wounds during a high-level mission. Special agent Vasu heads a division of RAW called TOCSI, which was tracking public enemy number one, simply referred to as MRS (Nawazuddin Siddiqui). MRS had the ambition of insulting Jaishankar Prasad(Mithun Chakraborty) and thus he wanted Vasu to slap him in public. However at the end, MRS fails in his Vrindavan temple blast and finally Vasu kills MRS by drowning him in River.
After finishing a successful meeting with his movie producers in Bangalore, Nanda, a jingles composer catches the highway to Chennai. On his way his car breaks down and he hitchhikes with Arjun, a businessman’s son on his way to the same destination. During their journey together they discuss their personal lives till Arjun proposes a deal; a deal that is marked with murder but promises to better their personal lives. However this deal does not work in Nanda’s favor and he soon finds himself in deeper complications.
Chotta (Daniel Balaji) is a terrorist, known for bombing various places in the past. He is currently jailed in a prison in Uttar Pradhesh, India. He escapes the jail by planting a bomb there and moves to various cities across India, while planting bombs everywhere, killing many people. His next target is Chennai and he heads towards the city to complete his mission. He often takes lifts from various vehicles across the highway. He communicates with his associates using a Gmail account, by composing his messages, saving them as drafts and providing the login details to his associates, who login later and delete the drafts meant for them after reading. Thus, their IP addresses remains untraced. The police issue a red-alert across the country and issue an order to arrest Chotta, all over India. His photo is faxed to all the police stations, who begin their search.
Bhavani (Sneha), an honest police officer in Hyderabad, is posted as Assistant Commissioner of Police in Tirunelveli upon the request of the Tamil Nadu government. The town is controlled by Sivalingam (Kota Srinivasa Rao), a baddie and aspiring politician who indulges in all unlawful activities. Bhavani resolves to put an end to all his acts. Meanwhile, Surya (Sampath Raj) voices against Sivalingam. As it happens, Sivalingam’s son Ranjith (Aryan) plays spoilsport in the life of Bhavani’s sister Deepa (Yasmin Khan). Efforts to prove him guilty by Bhavani end in vain. Now, a conspiracy is hatched by Bhavani in the company of Surya, and Ranjith is killed. An enraged Sivalingam takes Bhavani head-on. Sivalingam vows vengeance, and what happens from there forms the rest of the story.
Palakattu Madhavan (Vivek) is a lazy, irresponsible man. Embarrassed his wife Lakshmi (Sonia Agarwal) earns more than him, he quits his job out of spite. He then adopts the old woman Pattu Maami (Sheela) as a surrogate mother because she offers to pay cash for the opportunity. The character “Palakkattu Madhavan” is also an acknowledgement of a character with the same name in the movie Antha Ezhu Naatkal starring Bhagyaraj and Ambika.
A man, surrounded by birds, hangs himself to death at a cell tower. Elsewhere, the scientist Vaseegaran introduces Nila, his new humanoid robot, to a group of students. A little later, a student’s smartphone starts flying all on a sudden, exhibiting avian characteristics. Before long, cell phones all over Chennai begin to fly away, leaving the city in chaos. At an emergency council meeting initiated by the government, Vaseegaran enunciates that it is beyond conventional science to fight what he considers a fifth force, and proposes reinstating Chitti, which was dismantled in 2010. But Dhinendra Bohra, who lost his father, Professor Bohra, to Chitti’s anger,[a] opposes, and the council decides to seek help from the military, thereby vetoing Vaseegaran’s proposal.
The growing stream of cell phones leave havoc in its path, killing a mobile phone wholesaler Jayanth Kumar, a transmission tower owner Ranjit Lulla and the state’s telecom minister Vaira Moorthy. To prevent further damage, S. Vijay Kumar, the Home Minister, unofficially gives Vaseegaran permission to rebuild Chitti. Chitti traces the mobile phones, which have taken the form of a giant crow, and they fight, during which Chitti’s battery power is depleted and it starts searching for a power source amongst three huge signal transmitters. To Chitti’s surprise, the crow is unable to penetrate the field of transmitters and suffers damage while attempting to do so.