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.

Madhusoodhanan aka Madhu (Udhayanidhi Stalin) is a jobless software engineer, who recently lost his job due to recession. He is in love with Bhargavi (Manjima Mohan), a rich girl, who is under the care of her elder brother Dheena (R. K. Suresh), who is the Assistant Commissioner of Police. Dheena opposes their love primarily due to religion, while also not liking Madhu from first instance. Bhargavi urges Madhu that they should get register married before Dheena could stop them. Madhu being jobless, often borrows money from a notorious money lender, Kanthuvatti Murugan (Ravi Mariya) and fails to repay it on time. Hence, Murugan is in search of Madhu. Just before the day of his marriage, he borrows his friend's car and promises to return it soon.

Kulandai Velu (Soori) is a dubbing artist, who dubs for Chhota Bheem in Chennai. His wife lives in his native place and is expecting a child very soon. Kulandai promises to return to her soon, after completing the day's work. He starts heading to his native place late that night on his motorbike. Chotta meets Kulandai on the highway and asks for a lift. He obliges and also borrows Rs.200 to fill petrol at a petrol bunk for the bike. As they travel, they arrive near a police check post, who look for traffic violators. Chotta sees this and escapes thinking that they are looking for him. Kulandai is perplexed. After sometime, while Chotta asks for a lift from Madhu but he mistakenly hits Chotta and injures him. Madhu admits Chotta in a hospital and escapes from there, as he did not have enough money to pay the bill. Chotta also manages to escape the hospital and reaches his hideout place, a flat in an apartment building, owned by one of his associates, a lady who works as a manager, thus causing no doubts to anyone.

Meanwhile, the doctor, who treated Chotta in the hospital comes to know from the news that Chotta is a wanted terrorist and informs the police. The police collect the CCTV footage from the hospital and the highway, which contained Madhu and Kulandai providing lifts to Chotta. Hence, they corner and arrest both of them. While being taken to custody, they are hit by a jeep and are injured, causing Kulandai to forget his past. Madhu thinks that Kulandai must be a real associate of Chotta and if he can make Kulandai tell the police that Madhu is not involved in this case, then he can escape. However, he is shocked to see Kulandai having forgotten his past. The case is handled by Dheena, who now gets a good chance to reject Madhu, as he doubts that he is a terrorist. Dheena plans to kill both of them in an encounter, but Madhu and Kulandai manage to escape. With help from Bhargavi, they all hide in her friend's flat, which happens to be just below the flat in which Chotta is hiding, in the same apartment. Chotta plans his attack in two days and sends the bombs to his associates. He tells them that he will mention the locations one hour prior, using the draft communication.

Madhu and Bhargavi take Kulandai to a doctor, Thillai (M.S. Baskar) and try to regain his memory using hypnotherapy. Thillai successfully makes him regain his memory and he reveals that he too is innocent like Madhu. Madhu urges him to recall anything, while Kulandai gave lift to Chotta. Kulandai tells them that Chotta made a phone call from the petrol bunk's public phone and using lip reading, he manages to get the gmail username of Chotta and his associates. However, he could not get the password, as Chotta was turned the other side while saying that on the phone. With help from his friend in a telecom industry, Madhu gets the number to which Chotta made the call and tracks down the number to the same apartment in which they are currently staying at. He identifies Chotta and manages to grab him, but Chotta overpowers him and escapes. Madhu chases Chotta, but Chotta gets away with his female associate escapes in a car. Madhu throws his phone and manages to record a conversation between Chotta and his female associate. Chotta also delivers instructions to the bombers about the locations to be targeted via a draft from his Gmail account.

Madhu manages to get Chotta's laptop from the flat and they decide to go to the Police Commissioner's office. Meanwhile, Bhargavi informs Dheena that Chotta and the female associate are escaping. Dheena starts to chase them in his car and manages to shoot down the female associate, killing her, while injuring Chotta. Dheena arrests Chotta and bring him to the Police Commissioner's Office. The police use narcotics to get the password from Chotta and Madhu successfully logs into his Gmail account. He finds out about the plan. Since Chotta instructed the bombers to check the mail just one hour prior to the attack, the draft message remains unchecked by the bombers. Madhu deletes the drafts sent by Chotta and sends a new location detail to all of the four bombers, which happened to be the same location. As all the four bombers receive the draft by the next day, they go to the location which is a bus and plant the bombs, only to find out they have been set up. The bus is filled with police officers in disguise, who are in undercover work. They immediately arrest the four bombers and deactivate the bombs. Madhu is hailed as a hero for saving the city. Dheena also approves Madhu and gets Bhargavi married to him. Madhu manages to build his dream home. Dheena and his co-officers were transporting Chotta and the four bombers at a jail, but Dheena and his co-officers decide to kill all of them, as they are terrorists and do not deserve to live.