Raasu (Santhanam) and Mokkai (Ganja Karuppu) are youngsters sharing a hostel with a diverse group of people. Those people include Professor Mani (Madhan Bob), a staunch atheist named Thanjai Rudran (Rajesh), a poet, and other unemployed, struggling men. Raasu, who works in a coffee shop, is in love with Mahishasuramardhini (Madhumitha), but she seemingly ignores all his advances. Raasu was even attacked by her brother after hanging around her house for extended periods of time. Mokkai, who is unemployed due to his lack of education and does whatever job that he can find, dreams of marrying his uncle's daughter (cousin) back in his village.

After a particularly bad day where Mokkai is arrested and beaten by female police officers and Raasu's lies of being in a well-paid job are uncovered (to Mahishasuramardhini's disgust), the two are also kicked out of the hostel by the owner due to the inability to pay rent. On their last night, both vent their frustration at Kadavul (God) after heavy drinking. Both are shocked when Kadavul (Prakash Raj) appears in front of them. Mistaking Him for another unemployed fellow, the two head back to their hostel room only to find Him waiting for them in it, waving aside this miracle, all three fall asleep. The next morning, Kadavul finally manages to convince Raasu and Mokkai of His true identity after appearing in the forms of Vishnu, Jesus, and Buddha.

Armed with a "galaxy box" (access to a supercomputer) that is the source of His power, Kadavul makes a deal with Raasu and Mokkai. He will spend time with the two (under the name of Arnold and the identity of both Raasu and Mokkai's uncle), observing their day-to-day routines while advising them in the process, to see whether it is truly His fault for their poor standard of living, or their own. Arnold also manages to persuade the hostel owner to extend Raasu and Mokkai's stay for a week, while their bet is undertaken.

During the allotted time, both Raasu and Mokkai learn a great deal through Arnold's own actions and His teachings. In the meantime, Wellesley Prabhu (Ilavarasu), another hostel inhabitant, accidentally discovers "Arnold's" true identity, but is persuaded to keep silent. However, Arnold is in for a shock when on His last night with them, Raasu and Mokkai steal His "galaxy box" and use it to improve their lives. To Prabhu's despair, the true God is forced to lead an ordinary (yet underprivileged) life in the hostel. Raasu and Mokkai meanwhile find that their families, despite their gifts, remain highly suspicious of their wealth and ungrateful as well. They then start to use the box to inflict suffering on their past employers and those who refused to give them jobs. Ultimately, Raasu is once again rejected by Mahishasuramardhini, who turns out to be a prostitute, and throws the box into a bin in shock. Prabhu later recovers the box and hands it back over to Arnold. Although forgiven, Raasu and Mokkai feel deep regret for their actions and promise to turn their lives around, which they duly do. Both of them become successful people in later life, along with Prabhu and various other characters.

A few years later, Arnold once again comes to the same room, to help another group of youngsters staying there and lamenting their current situation. This time, Arnold keeps His "galaxy box" bound in chains in His pocket to make sure that it is not stolen or misused like before. Arnold smiles at the camera as the film ends.