A young boy named Ranadheeran "Rana", who hails from the kingdom of Kottaipattinam, leaves his family for good, despite his brother Sena pleading him not to do so. The boy soon meets with an accident while rowing in the river and is eventually discovered by some fishermen from the neighbouring kingdom of Kalingapuri, a bitter rival of Kottaipattinam. He grows up there and trains as a warrior, becoming a fearless warrior by the time he is an adult. Due to his fighting skills and bravery, he soon wins the confidence of the ruler of Kalingapuri, Raja Mahendran, who promotes him to Commander-in-Chief of the Kalingapuri army. Rana?s first job as Commander-in-Chief is to free the soldiers of Kottaipattinam, who are being treated as slaves by Raja Mahendran, enlist them in the army and train them. He then seeks the permission of Raja Mahendran to attack Kottaipattinam, to which the latter agrees. However, during the war, Rana encounters his childhood friend Sengodagan, the son of the Maharaja of Kottaipattinam, Rishikodagan. Immediately signalling an end to the war, he along with the soldiers disown Kalingapuri and return to Kottaipattinam, much to the disgust of Raja Mahendran and his son Veera Mahendran, who swear revenge on Rana for tricking them and betraying Kalingapuri.
At Kottaipattinam, Rana and Sengodagan renew their friendship. Sengodagan introduces Rana to Rishikodagan, who is alarmed on seeing him. Rana also reunites with his younger sister Yamuna Devi (whom he last saw as a baby) and their uncle, who raised her, but soon learns that his mother Yaahavi is dead and Sena is missing. He soon learns that Yamuna and Sengodagan are in love with each other. He accepts their relationship and decides to get them married, even cleverly convincing Rishikodagan, who is unwilling to get his son married to a girl of a non-royal family, to agree to the marriage. Meanwhile, Rana also falls in love with his childhood sweetheart Vadhana, the daughter of Rishikodagan.
Soon, Sengodagan and Yamuna get married. But following the wedding, Rishikodagan disowns his son for marrying Yamuna despite knowing that the latter does not belong to a royal family. An unfazed Sengodagan immediately walks out of the palace with Yamuna. Later that night, a masked man barges into the palace and attempts to kill Rishikodagan. Vadhana immediately goes after him, fights him and gets him captured. Rishikodagan unmasks the assassin who is revealed to be Rana, and immediately throws him into prison, sentencing him to death. An upset Vadhana rushes to the cell where Rana is imprisoned, where Rana tells her why he attempted to kill Rishikodagan.
Rana is the younger son of Kochadaiiyaan, the former Commander-in-Chief of Kottaipattinam?s army. Kochadaiiyaan was extremely respected in Kottaipattinam for his bravery and exploits and was more popular than Rishikodagan himself. This made Rishikodagan jealous of Kochadaiiyaan. One night, when Kochadaiiyaan was returning by ship to Kottaipati?nam with his army (the men who were the slaves of Raja Mahendran in Kalingapuri) after buying horses and ammunition, they were attacked by the army from Kalingapuri. Kochadaiiyaan defeated them but allowed the rival army? men to return to their kingdom as an act of chivalry, instead of killing them. However, the Kalingapuri army, before leaving, poisoned the food on the ship. The Kottaipattinam army men consumed this food, and fell ill.
Despite knowing that it was the work of the Kalingapuri army, Kochadaiiyaan immediately rushed to Kalingapuri because it is the only land body close enough to provide medicines to the sick and dying soldiers. He ordered Raja Mahendran to provide his soldiers medical assistance. Raja Mahendran in turn cunningly asked Kochadaiiyan to leave all the horses, ammunition and the sick army men in Kalingapuri with a promise to cure them and keep them as slaves instead. Kochadaiiyan thought that his men rather be alive as slaves than die from poisoning, and also felt that when they officially wage a war in the near future, all of them could be easily rescued. So he accepted Raja Mahendran?s offer and left Kalingapuri all alone. When he returned to Kottaipattinam, he was sentenced to death by a jealous Rishikodagan, on the grounds of being a traitor to Kottaipattinam by surrendering his army men, horses and ammunition to Kalingapuri. Though all his subjects were dismayed at Kochadaiiyaan being sentenced to death, with Yaahavi even going to the extent of publicly rebuking Rishikodagan for his injustice, the latter stood firm in his decision. Kochadaiiyaan was executed the following morning before Rana?s eyes. After this, Rana ran away to Kalingapuri with the intention of freeing the soldiers of Kottaipattinam and taking revenge on Rishikodagan for unjustly killing his father.
Vadhana is shocked on hearing about her father?s actions and reconciles with Rana. She then pleads with her father to release Rana to no avail. Meanwhile, Rana escapes from prison. When Rishikodagan learns about Rana?s escape, he immediately arranges for Vadhana?s marriage with Veera Mahendran after consulting with an astrologer and learning that his life is at Rana?s mercy. Despite the enmity between Kottaipattinam and Kalingapuri, he does this with the hope that their united armies and their mutual hatred for Rana can subdue him.
On the day of the marriage, Rana arrives just when the marriage is about to take place. He and the people of Kottapattinam berate Rishikodagan for surrendering to Kalingapuri for his own interests (the same charge which Rishikodagan had placed on Kochadaiiyaan years ago), following which a war starts between Rana and the united armies of Kottaipattinam and Kalingapuri. Rana successfully manages to subdue the armies of both kingdoms, as well as Raja Mahendran and Veera Mahendran. He then battles Rishikodagan, who he eventually decapitates.
As Rana and Vadhana reunite, a young soldier comes towards them riding a horse. This soldier is revealed to be Sena, and both the brothers reunite.