C. Prem Kumar, Saras, Balaji Tharaneetharan alias Bhaji, and Bagavathi Perumal alias Bucks are close friends. Prem is about to be married to his fiancée Dhanalakshmi. Two days before his marriage, the group of friends decide to play a game of cricket. During the game, Prem attempts to catch a ball hit by Bhaji but instead, he drops it and falls on the back of his head but gets back up and says he is fine. After the game, the friends realise that Prem has been muttering the events leading to his injury over and over again. Initially, they think Prem is trying to prank them but later at Bucks' house, they realise that something is wrong. They realise that Prem is suffering from temporary memory loss due to the injury and has forgotten the past year of his life including his upcoming marriage, Dhana, and even his bike that was stolen a few days back. However, he still recognises his friends.

Worried, the trio takes Prem to a local hospital where the doctor diagnoses him with anterograde amnesia or short-term memory loss and checks him into the hospital. They decide to keep his parents and Dhana in the dark. Bucks' boss arrives at the hospital and recounts the story of a man he knew who developed amnesia after an accident and never recovered. Petrified, the trio decides to leave Bhaji in charge of Prem for the night with the hope he will recover the next day but the following morning he continues to remain in the same condition. With his wedding reception that evening and the doctor not allowing him to get discharged, Prem is snuck out of the hospital by the trio. They take him to a hair salon to get him ready for the marriage but are shocked to see Prem's father there. However, they manage to keep Prem's condition a secret from him. They then take him to his home and luckily nobody suspects anything amiss.

At the wedding reception, the trio finds it challenging to keep Dhana and Prem together since he remembers nothing about her. He keeps remarking how awful Dhana looks, much to her dismay; however, the friends are able to control the situation. Much to Bhaji and Bucks' surprise, Prem starts to obey Saras' commands without questioning. Later that night, Saras reveals that he helped Prem complete his schoolwork during high school and since then Prem has always respected Saras more than anyone. The next day at the marriage, the trio finds themselves in a fix when Prem refuses to tie the wedding knot citing the reason that he does not know Dhana and says he cannot forget about a girl he once liked in school. Miraculously, after much persuasion by Saras, he ties the wedding knot. Tears of happiness flow from the friends' eyes, however, their relief is temporary as Prem's condition worsens.

The trio take Prem back to the hospital where they are reprimanded by the doctor for sneaking him out. However, he is surprised to know that the wedding was a success. He realises that Prem has not slept well the past few days and gives him sleeping pills to help him sleep. The next day Prem's condition seems to be the same but later he recounts everything revealing he has recovered and that his memory is back. The friends celebrate, much to Prem's confusion. He is surprised to know that his wedding is over and laments how much he looked forward to his wedding but now is unable to remember it. Finally, the elated friends return home with Prem.