Athithi is based on the Malayalam movie Cocktail, itself borrowing elements from Butterfly On A Wheel, and centers around Mathiazhagan (Nandaa) and Vasuki (Ananya), whose seemingly normal existence is shattered when a mysterious stranger (Nikesh Ram, who delivers a stiff performance) enters their lives. He informs them that he possesses information about their daughter’s well-being and presents them with bizarre dema…