CATAMARAN revolves around the Tsunami-affected lives of the middle-aged Singaram, who is now taking care of his orphaned niece Anandhi, who is a teacher, and nephew Mani, who are the children of his elder and younger sisters, respectively. As the fisherman Singaram works hard to provide for his family, he also tries to arrange a groom for his niece, who rejects the many alliances he suggests. Once on an impulse, when he proposes to his niece, she is shocked. Singaram soon comes to know that she is in love with a fellow female teacher, Kavita. As Singaram comes to terms with his niece's sexual orientation, he is ostracized by his community because of her sexual transgression. The patriarchal Singaram's ego is deflated, and he empathizes with the plight of the village barber, the transwoman Alankaram.