Ajamukhi (G. Sakuntala) sister of Soorabadman (S.A. Ashokan) the Asuran (Demon) king of Veeramahendrapuri tries to take away Indrani (S. Varalakshmi), wife of Lord Brahma forcefully for her brother. Brahma's loyal escorts defend their queen and cut off Ajamukhi's hand. Soorabadman, who has many God-given powers gets angry, and sends his brother Thaaragasuran (S.V. Ramadas) and his army to capture the Devas (Amarargal) and torture them. Lord Shiva (Gemini Ganesan) and Parvathi (Savithri Ganesh) are furious and Lord Shiva uses six of his powers, integrates them to create a boy called Murugan. Murugan in six avatars is brought up by six Karthikeyas (women). Murugan grows up and Parvathi reunites the six children to create Lord Kandhan (Master Sridhar) with six faces while the divine girls are rewarded by being transformed into stars. As he was brought up by Karthikeyas, Kandhan is also called Karthikeyan or Arumugam.
When Lord Brahma comes to meet Lord Shiva at Kailasam, his abode, he ignores Murugan which upsets him and when Lord Brahma returns, Murugan demands an explanation for some mantras for which Brahma has no answer and Murugan arrests him. Lord Shiva intervenes and releases Brahma. Murugan then teaches the secret mantra Om' to Lord Shiva. Murugan also teaches a lesson to Awaiyar (KB. Sundarambal) who is proud of her knowledge.
Years pass by and Soorabadman continues torturing Amarargal. Lord Shiva tells the young Murugan (Sivakumar) to wage a war with Soorabadman. Parvathi using her powers creates Sakthivel (spear), a weapon to destroy Soorabadman. Shiva also sends a valorous Veerabaghu (Sivaji Ganesan) and his brothers to aid Murugan. Murugan sends Veerabaghu as a peace ambassador to meet Soorabadman. Veerabaghu explains the implications of taking on Murugan to Soorabadman but he refuses to heed. So Murugan advises Veerabaghu to start the war and Murugan using the Shaktivel given by his mother first destroys Thaaragasuran's Kavinga Mountains which were the entry point to the kingdom.
Murugan's army is led by Veerabhagu. Soorabadman's army, led by his son Banugopan (K Balaji) loses in the first-day war and returns the next day to be killed by Murugan. Next day, Soorabadman's brother Singamugan goes for the war and Soorabadman joins him. In an intense battle, Murugan defeats Soorabadman and gives him an ultimatum to reform and come the next day. The entire Asura community is killed in the war. The next day, Soorabadman uses his powers and hides in various places to mislead Murugan. Finally, Soorabadman hides inside a tree and Murugan splits open the tree using the Shaktivel and kills Soorabadman. He transforms one part of the tree as a peacock and the other as a cock. The place where Murugan killed Soorabadman is named Tiruchendur. Lord Brahma and Indrani offer their daughter Deivayanai (K.R. Vijaya) to Murugan as a reward for his victory. Their marriage takes place and after a few days, Murugan decides to visit Thanigaimalai to marry Valli (Jayalalithaa), who has taken this birth just to marry him. Valli is at the fields and Vanji (Jayalalithaa again), a village astrologer, meets her and predicts that Valli will marry Lord Murugan soon. Murugan arrives there marries Valli and brings her home. Deivayanai gets upset with Murugan for marrying another woman. Valli too gets upset to know that Murugan is already married. Both Valli and Deivayanai complain about Murugan to Veerabaghu. Murugan clarifies that they were sisters Amudavalli and Sundaravalli in their previous birth, and both yearned to marry Lord Murugan and hence he married them both. Both understand and accept each other. Murugan then meets Nakkeerar (Seergazhi Govindarajan), who is writing an Aattrupadai on Murugan. Nakkeerar summarises all the main events in the life of Murugan and Lord Murugan is happy with Nakkeerar's effort and along with Valli and Deivayani blesses him.
[from the book Pride of Tamil Cinema: 1931 to 2013 by G Dhananjayan, Blue Ocean Publishers, 2014]