Ulkuthu is set in a small coastal town which is ruled by Kaka Mani (Sharath Lohitashwa) and his brother Saravanan (Dhilip Subbarayan), loansharks who deal in blood and blows when their debtors don’t pay on time.

Onti, a carefree young man, catches the eye of a gangster, Silk after he saves Paaru from him. In retaliation, Silk murders Onti’s dear friend which sets Onti on the path of revenge.

Kathir (Bobby Simha) has an interest for Anbu (Tanya Ravichandran), but due to family situations, she gets hitched to Karuppan (Vijay Sethupathi). What does Kathir do, to separate Karuppan and Anbu, and does he finally get to marry Anbu?