An ardent Rajnikanth fan, postman Raja skips his duty of delivering the last eight letters and goes to watch Rajini’s latest release. Later that evening, he meets with an accident and slips into coma. When Raja wakes up after 23 long years, he remembers about those undelivered letters and gets on to his bicycle to deliver them. His daughter, Rajini, joins him.

In 1995, Rishi posts a suicide letter for his mother. In the meanwhile, Santosh, a man in his 40s, kidnaps two older men. When Raja finally delivers Rishi's letter, his mother hands it over to Santosh, unaware that Santosh is wanted by the cops. What will Santosh do? When Raja realises that he's in a trap, will he manage to escape?

The second letter that Raja has to deliver is to scientist Dr. Isaac. The letter is written by Dr. Issac's wife who leaves him for his negligence when he fails to take care of her while she is pregnant. What happens when Raja and his daughter Rajini take the letter to Dr. Isaac who's now old and has developed a dissociative personality disorder? Incidentally, Rajini tells Raja that she is adopted and seeks information about her real parents. Raja, unable to recover any information, passes out.

In 1995, Anitha writes a letter to Dr. Chandrasekar. When Raja and Rajini deliver the letter to him, he gets nostalgic about his time with Anitha. He remembers his college days, their love, and how she broke up after she was diagnosed with brain tumor. After hearing his story, Rajini and Raja help Chandrashekar attend his college reunion and meet Anitha.

Twenty-three years ago, before Raja became unconscious, Sameer and Vidya had applied for a divorce, leaving their son with Vidya's brother Dr. Vishwa. Later, their son died of a seizure attack. When Raja meets Sameer after he regains his consciousness and hands him the pending letter, Sameer realises that it's from his son. He goes into a state of shock after reading it.

Raja and Rajini take the next letter to John. After reading it, John reveals that it's a letter from his father who wanted to meet him one last time. In the meanwhile, Rajini notes the ‘from' address and visits the old age home where John's father lived. To their surprise, John has already reached there. The caretaker informs John that his father has passed away, and hands him a bag full of money that his father had left behind. The caretaker also reveals a story that John’s dying father had told him, and that makes John and Raja feel a deep sense of guilt.

Vishal, the person to whom the sixth letter is addressed to, is agitated upon reading the letter since it was the answer to his search for his lost family. As Vishal prepares to leave for Coimbatore to follow up on the letter, Rajini and Raja accompany him.

Ibrahim and Ravishankar, two best friends, used to communicate through letters after they were seperated in their childhood. Raja finds one such undelivered letter with him. When he and Rajini set out to deliver the letter, they discover that the person the letter is addressed to has grown very old!

In 1995, a man explains to his four sons the philosophy of not desiring another person's possession by citing the 'Thirukural' poem as an example. When Raja finds a letter addressed to Mr. Sakthivel, he and Rajini reach the location to hand over the letter to him. Instead, the letter is received by his brother, Mr. Rajavel. But the contents of the letter force Raja and Rajini to set out on a path to find Mr. Sakthivel.

Rajini and Raja have now delivered all the eight letters but the duo still needs to resolve a mystery from one of the letters. When Raja tries to do this, it turns out to be the most emotional moment for Rajini. What letter is this and will Raja, the postman, be able to solve the mystery?