Saravanan (Vishal) is a person in Ooty who runs a business of gathering people for politicians. One day he met Maya (Hansika) and fell for her. However, Rajshekar (Santhanam) also falls in love with her. Saravanan convinced Rajshekar to not fall for Maya by talking about the expenses high class people require. Rajshekar is a police inspector. Due to several mishaps caused, he was fired and started working as a hotel doorman. He was shocked to find Saravanan and Maya going out together. He asked Saravanan how he made Maya to fall in love with him. As Saravanan finished his story it was revealed that it was Saravanan who indirectly caused those mishaps to Rajshekar. Rajshekar enraged hired Kumaran (Vaibhav), who is a specialist in breaking other's love. Kumaran then sends Andrea Jeremiah who shows an edited photo of her and Saravanan together and how a child mistook Saravanan for her father. This causes a conflict in the relationship of Saravanan and Maya. Due to love failure Saravanan consumed alcohol and was unconscious. Kumaran who was also at the bar helped Saravanan and dropped him at his house. Saravanan's mother, Thulasi (Tulasi) who was ashamed of Saravanan's behaviour send him to meet his father Aalavanthan (Prabhu) and his younger brother Shakti (Sathish) at Madurai.There they meet Alavanthan and rejoins him. They also come to know that Kumaran is also the son of Alavanthan's ex- lover. Alavanthan reveals to his sons that they have 3 aunts (Ramya Krishnan), (Aishwarya), (Kiran Rathod). Alavanthan wants his sons to marry the daughters of their aunts so that their family could reunite once and for all. At first Saravanan hesitates but when he finds Maya is also a daughter of his aunt he agrees to the plan. The village people mistook them as police posted to their village, which helps the trio to sneak into their aunts house. There their uncles help them to create affection to their daughters. Their aunts daughters also starts to reciprocate love to the trio. Their elder aunt (Ramya Krishnan) decides to participate in the MLA election in their provinces, but villan Pasupathy current MLA of the provinces and ex-servant of Alavanthan's family provokes her by saying that if he lose to her he will work at her home as servant but if she loses her daughter Maya will be married to his son. Saravanan then helps his aunt to win the elections. However a few days before the elections Saravanan's aunts find out that saravanan's father is their brother Alavanthan who was seen as the murderer of their father. their hatred towards Alavanthaan results in them getting Saravanan and his brothers caught in police and Alavanthaan is hurt by his sisters' harsh words at him. He suddenly got a heart attack and is admitted in the hosipital. As Saravanan and his brothers are stuck in jail, his aunt had lost many of the peoples hope for voting her due to Pasupathy's evil plans in causing misunderstandings. Then Sarvanan uses RDX, to stop Pasputhy's evil plans. Then when Pasaputhy tries to bribe people with money, Sarvanan and Kumaran cause some mishap and the tables turn giving Periya Poonu the edge. There Pasupathy comes with a mob and tries to kill the whole family and take Maya, but Sarvanan and Maya unite in a different location, and then fights Pasupathy and his son giving the victory. It was also revieled that Pasupathy killed Aalavanthan's father not Aalavanthan. There Aalavanthan and the whole family unite, and Maya weds Saravanan.
Venkat Ramakrishnan (Srikanth), Sevarkodi Senthil (Jiiva) and Panchavan Parivendan aka Pari (Vijay) are three first year engineering students who share a room in the hostel of Ideal Engineering College (IEC), Chennai. Venkat studies engineering to pursue his father's wishes over his own wish – to become a wildlife photographer, while Senthil studies engineering to get his family out of poverty. Pari, on the other hand, studies engineering for his simple passion for machines and devices. He believes that one should follow excellence, not success, as success will take care of itself if excellence is followed. However, this approach to studies is sneered upon by the dean of the college, Professor Virumandi "Virus" Santhanam (Sathyaraj). Virus and the faculty favour Pari's classmate, an NRI student Srivatsan aka "Silencer" (Sathyan), who believes in mindless rote learning over understanding to reach his goals of corporate status. Pari constantly spars with Virus and Silencer due to their differences in their educational approaches.
Arjun (Silambarasan), an animation artist living in London with his uncle (Ganesh), meets Nisha (Varalaxmi Sarathkumar) in a London pub. She is an aspiring dancer who is living with her aunt (Shobana). After going around together for a day, Nisha proposes a relationship and Arjun agrees. Arjun hates Nisha attending salsa classes with her friend Mojo as her partner. However, he agrees to marry her.
At the Kanyakumari beach, Geetha (Shriya Saran) looks at a lonely lying personal diary where she enjoys a poem written in it. She admires the poem by replying on the same page. While she and her friend admire the beauty of Sunrise, she accidentally loses one of her anklets (it falls in the sea). She sees a person jumping in after it and she perceives him to have died in the waters. The incident haunts her in her dream again and again and feels very guilty for it. In her college, she meets a rich, handsome boy Arjun (Sameer Dattani) who impresses her to win her love. He proposes her and threatens her to love him or else he would die by jumping from college roof top. Already feeling guilty for being cause of a person's death, not willing to let it happen again Geetha accepts his love and screams 'I love You' in front of the entire college to Arjun which was witnessed by Kutty (Dhanush).
Rajaraman, nicknamed "Vasool Raja" (Kamal Haasan) is a local don in Chennai, making a living by collecting money from people who refuse or dilly-dally in paying their debts to others, with the help of his right hand man Vaddi (Prabhu Ganesan). Given that his father had wished him to be a doctor, he creates the faux Venkataraman Charitable Hospital (named after his father) and pretends to live in accordance with this wish whenever his father (Nagesh) and mother Kasturi (Rohini Hattangadi) visit him in Chennai.
Sakthi (Vijay) is the adopted son of a Madurai-based don Sivan (Mohanlal) and is also his right-hand man, bodyguard and driver. He hates the police due to a police officer killing his father, who was Sivan's driver, in his childhood. His hatred is such that he hates the khaki colour (which is worn by policemen in India), constantly teases his friend Gopal (Soori), who is a Sub-inspector and even loses romantic interest on a woman named Shanthi (Kajal Aggarwal) after he finds out that she is a police inspector. However, when Sivan is insulted by the new Police Commissioner of Madurai (Pradeep Rawat), he forces Sakthi to become an IPS officer to save his crime syndicate and prove the Commissioner's words wrong (A policeman can think like a criminal, but a criminal can never think like a policeman). Reluctantly Sakthi passes all the tests and training in Civil service exams without any effort (due to high political influence). He takes charge as Assistant Commissioner of Police [law and order] of Madurai center, Sakthi gives free rein to Sivan and his henchmen, who wreak havoc over Madurai, until one of their activities inadvertently causes a gas leak which destroys a school and some nearby buildings, killing several people, including women and children. This incident, compounded by the assault of a woman (Meenal), whose husband was killed in the gas leak, by Sivan's henchmen when she had come to the police station to lodge a complaint against Sivan, causes Sakthi to take up the path of an honest and upright police officer. Sakthi's new persona is not liked by Sivan and after a heated argument between the two, he disowns Sakthi. A cat-and-mouse game then begins between Sivan and Sakthi, with Sivan, his henchmen and his family determined to humiliate Sakthi at every opportunity, while Sakthi, assisted by Shanthi and Gopal, tries to rid Madurai of Sivan's influence. Sakthi is soon promoted to Deputy Commissioner of Police for his efforts.
Bergmans (Arjun), a brilliant but unruly student, is thrown out of his seminary for committing the sin of the flesh after being caught red-handed by fellow student Sam Fernando (Arvind Swamy). Blaming the good-hearted Sam for his ouster, Bergmans vows revenge and challenges to prove that evil does reign supreme in this world. Sam finishes his education and training and arrives at a village as the new Father of the local church. A local boy named Thomas of this village who is the illegitimate son of a local fisherman (Ponvannan) has grown up in a rough neighbourhood, following the death of his mother and thus being forced to fend for himself.
Ramachandran (Sachin Khedekar) is a genetic scientist who doesn't get due credit and funds for his research. He tries creating a human with several talents through baby designing, which thus leads to the birth of his sons, who are conjoined together above the waist. Since they share a common heart, doctors suggest a sacrificial surgery, to which their mother Sudha (Tara) objects. They begin raising their children, Vimalan and Akhilan (both played by Suriya). In the following years, Ramachandran makes it big with the help of Sudha. His company, Locus Lacto Products, makes huge profit through their product "Energion", the top-selling children’s powdered milk energy drink in the market.
Jagadish (Vijay), a captain in the Indian Army, returns to Mumbai from Kashmir. On his arrival, his parents and younger sisters force him to see Nisha (Kajal Aggarwal), who they choose for him to be married to. At the bride-viewing ceremony, Jagadish makes up excuses to avoid marrying her, which includes commenting about her being old-fashioned. On the contrary, Nisha is a college-level boxer, who is completely modern in her outlook. Jagadish realises this and proposes to her, which she reciprocates.
'Anal' Murugan (Vikram) a gym boy who dreams of becoming a successful villain in films lives along with Thambi Ramaiah and his gym co-boys. He bumps into an old man Dakshinamoorthy (K. Vishwanath) who is under pressure from his son Chidambaram (Avinash) to sell his orphanage to a scheming lady politician Ranganayaki (Sana) who is majorly into land grabbing along with her hatchet man 'Vaappa' Abdul Kadhir (Pradeep Rawat). Murugan eventually falls in love with Dharshini (Deeksha Seth). The one-man army Murugan becomes the Dakshinamoorthy’s saviour as Ranganayaki and her men are after them. How Murugan single-handedly fights the powerful politician and brings them to light forms the rest of the story.
Karthik Swaminathan (Dhanush), referred to as 'Genius' by his friends, is a freelance photographer who aspires to become a wildlife photographer like Madhesh Krishnasamy (Raviprakash). His close friends Sundar (Sunder Ramu), Shankar (Mathivanan Rajendran), Padmini (Pooja Devariya) and Vindhya (Shilpi Kiran) support him and his sister after the death of their parents. One day, Sundar introduces Yamini (Richa Gangopadhyay) as his girlfriend to Karthik and his friends. On their first meeting, Karthik and Yamini have a bitter experience but they slowly develop a special bond. Karthik tries to stay away from the girl since he does not want to break his friend's heart, but a sequence of events brings them closer. Eventually, Sunder's dad arranges for Karthik and Yamini to be married.
After a decade of research, the scientist Dr. Vaseegaran creates a sophisticated android robot with the help of his assistants, Siva and Ravi, in order 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 terrorist organisation, but has so far been unsuccessful.
Ambujakshi alias "Ambu" (Trisha), a film actress, arrives in Europe to spend the vacations with her friend Deepa (Sangeetha), a divorcee and her two children. While going in a taxi, Ambu recalls an early incident regarding her ex-boyfriend Madanagopal alias Madan (Madhavan), a wealthy entrepreneur: Three years ago, she was shooting for a film with actor Surya in a bright park and Madan was suspicious of her relationship with the actor. While returning, he lets Ambu drive his new car. Madan advised Ambu to stop acting, but Ambu claimed it as her profession which she can't give up, leading to an argument that caused their car to crash near a rock. At the same time they blamed a small white car that just passed by, to be the reason for the crash. Unable to bear any more arguments, Ambu broke her relationship with Madan and walked away.