During the 10th century, the Chola dynasty flourishes in South India, ruled by Emperor Sundara Chola (Prakash Raj](/actor/prakash-raj)). Sundara’s sons, Aditha Karikalan (Chiyaan Vikram) and Arulmozhi Varman (Jayam Ravi), are commanding the empire’s campaigns in Kanchi and Lanka respectively. Aditha mercifully spares the life of the Kanchi king, Khottiga (Babu Anthony), who desires a noble death instead of living in humiliation.
Sensing treachery within the court, Aditha dispatches his friend, the witty and courageous Vandiyadevan (Karthi](/actor/karthi)), who belongs to the Vaanar clan, to uncover the truth and report back to his sister, Princess Kundavai (Trisha Krishnan) and Emperor Sundara. Upon arriving at the Kadamboor fort, Vandiyadevan overhears a conspiracy led by the emperor's treasurer, Periya Pazhuvettaraiyar (R. Sarathkumar), and other courtiers plotting to prevent Aditha from ascending the throne in favor of his uncle, Madhurantaka Chola (ahman), who is considered a rightful heir.
As Vandiyadevan seeks more information, he encounters Azhwarkadiyan Nambi ([Jayaram), a Veera Vaishnavite spy. After learning that Nambi's foster sister, Nandini (Aishwarya Rai), had mysteriously married Pazhuvettaraiyar, Vandiyadevan is drawn deeper into the royal intrigues. With Nandini's guidance, he enters the palace, revealing the conspirators to Emperor Sundara, despite constant threats to his safety.
In Thanjavur, tensions escalate as Kundavai insistently orders Vandiyadevan to contact Nandini before informing Aditha. The court becomes rife with manipulated beliefs about the crown prince plotting against the throne, led by Pazhuvettaraiyar and his associates. Kundavai, meanwhile, expresses concern about the kingdoms uniting in a familia competition for matrimonial alliances, promising that Arulmozhi belongs to her.
After Aditha’s victories, his feelings for Nandini surface, revealing a tumultuous past intertwined with love and vengeance. Nandini, motivated by revenge for her unjust treatment and Aditha's past actions against those she loves, conspires to keep both brothers from returning to Thanjavur.
Meanwhile, Ponniyin Selvan encounters Vandiyadevan in Lanka, where they strategize to send messages to Kundavai and Vanathi (Sobhita Dhulipala). Amidst more plots and royal feasts, Kundavai strives to protect her family while trying to rally support against the looming threats.
As Nandini and Pazhuvettaraiyar tighten their grip on power, increasing pressures lead to significant conflicts, including an attempted ambush on Ponniyin Selvan. With the stakes rising, Vandiyadevan and Ponniyin Selvan race against time to uncover the schemes that could jeopardize the throne while battling enemies from every direction.
In a dramatic and wrenching turn, a catastrophic storm leads to presuming the deaths of Ponniyin Selvan and Vandiyadevan, compelling Aditha Karikalan to swear vengeance against Nandini. With the news bringing devastation to Sundara, Kundavai, and Aditha, the twisted fate of their kingdom hangs perilously in the balance. Meanwhile, Oomai Rani (or Singala Naachiyaar) (Aishwarya Rai), the mute queen and Nandini’s mother, remains entangled in this treachery, desperately seeking rescue for Ponniyin Selvan from the depths of the sea.
