Set in the rural milieu of Tanjore, Rasa Manthiri kicks off from the word go, hinting at what's in store for the audience. A simple middle-class family — an over-sentimental father (Nadodigal Gopal), a concerned mother (Meenakshi), and two brothers, Surya (Kaali Venkat) and Karthi (Kalaiyarasan) — which is content cherishing the small joys in life. However, the marriage of 30-something Surya, has been a worrying factor for them for a while, and things are not working in favour of him. He becomes a laughing stock among the public, though he is hopeful of winning a woman's heart. Karthi, too, takes potshots at his elder brother Surya often for his marriage proposals repeatedly going haywire, adding to the woes.

In an unexpected turn of events, cupid strikes Surya and he falls head over heels for his neighbour Mahalakshmi (Vaishali). Though he is over the moon and puts his best foot forward to impress her, he sees a potential competitor in his younger brother, after the latter tries to move closely with the girl, only to annoy the former. Quite skeptical over Karthi's intentions, Surya ensures that Karthi gets admission in a college which is a little far away from their home. But, lady luck fails to smile on him for the umpteenth time, after he messes up his chance with a hasty decision. Meanwhile, Karthi falls in love with his classmate Subha (Shaalin) and starts dreaming of a life with her.

The audiences are in for a surprise when a dejected Surya moves on, and gives a nod to a bride whom he likes at first sight. But, the real twist is revealed when the viewers are shown who the bride is. The story then dwells on how Surya pins hopes on a married life with the girl whom he was impressed with, Karthi's struggle to win his love with the help of his friend Sathish (Bala Saravanan), and how interestingly both these tracks are intertwined.
Kaali Venkat as a naive, breadwinner of the family fits perfectly into the role, puts up an impressive performance, and is the show-stealer of the film. Kalaiyarasan is decent, and so are the heroines. The character artistes appear real and are apt for the story. PG Muthaiah deserves mention for his cinematography, which has captured the rustic beauty of the village, while Justin Prabhakaran does not impress except for a song. The film, overall, is a harmless entertainer if you go without expectations.