Madhiazhagan (Nandha) is a highly successful project manager at a leading property promoters firm. He’s happily wedded to Vasugi (Ananya) and has a five-year-old daughter Pavi. Posh house, heftily paying job, highly appreciative and supportive boss, and a happy family – Madhi’s life is a far fetched dream to most people in this era. But all changes one day, when a man requests to be dropped en route, when Madhi and Vasu set out on a pleasant weekend. The mysterious stranger pulls out a pistol and begins to threaten the couple to bend to his wishes, holding Pavi as hostage. And the day sets off with the stranger making the couple draw out all the money Madhi has, to the last penny and setting it all on fire. Next, he makes Madhi lose his career by leaking the top secrets of his company, trusted to him, to their competitor. And the day goes on with further more gimmicks by the stranger, while the couple are cornered to do it all for their little daughter’s life. And for the same reason, they also refrain from making a complaint to the police, although they are tantalizingly near their target. While this seems endless, how they figure a way out of the mess, with a completely unexpected twist to the whole story in the end, ‘Athithi’ is an edge-of-the-seat realistic thriller.

Sakthivel (Kamal Haasan) returns home to his father Periya Thevar’s (Sivaji Ganesan) village in Tamil Nadu after completing his education in London. Much to his father’s annoyance, he brings his westernized girlfriend Bhanu (Gautami) with him to meet his family. Periya Thevar is deeply offended since it is a tradition that the family elders choose the youngster’s spouses. To make things worse, Sakthivel reveals his plans on opening a chain of restaurants in Chennai which saddens Periya Thevar as he wanted his son to help the villagers improve their lifestyle with his level of education.

Bairavaa (Kala Bhairava in Telugu version) (Vijay), a collection agent for ICCI Bank in Chennai (Vijayawada in Telugu version), is a righteous person who is willing to employ even violent means to get back the money from the debtors. During his manager’s daughter’s wedding, he comes across Malarvizhi (Keerthy Suresh), a medical student from Kallidaikurichi in Tirunelveli district (Vishakhapatnam in Telugu version), and immediately falls in love with her. Malar goes to the Koyambedu bus station to leave Chennai, where Bairavaa comes to propose his love, when he notices she is cornered by a group of thugs with intent to kill her, as she was allegedly involved in an attack on a union minister’s son Charan (Roshan Basheer). However, they retreat after receiving a call from Periyakannu alias PK (Jagapathi Babu) from Tirunelveli, who tells them not to harm her.