The film is a sequel to Ong Bak 2 (2008) and revolves around Tien (Tony Jaa), who escapes after being captured by the Lord Rajasena (Sarunyu Wongkrajang) and recovers from his crippling injuries with the help of Master Bua (Nirut Sirijanya), where he returns to confront Bhuti Sangkha (Dan Chupong), who has replaced Rajasena as the king.

He momentarily fights back when they try to beat him with wooden staves, but they manage to submit him, and Rajasena orders Tien's elbows and knees to be snapped.

In order to find a solution, Master Bua initiates a Buddhist pilgrimage, in which it's revealed that the source of the curse is Bhuti Sangkha, the dark mystic that defeated Tien.

While Rajasena sleeps, the remnants of the Pha Beek Khrut bandits attempt to free Tien, but Bhuti appears and kills them.

Believing that a traitor informed Ayutthaya, the lord's ministers send assassins to kill Tien, but the attempt is thwarted by the sacrifice of the royal messengers.

The returning Master Bua announces that Tien suffered his fate due to negative karma, and he enlists the entire village to make merits to heal him back to life.

The process, which includes the making of the Ong Bak Buddha, is successful, but upon waking up, Tien discovers he is still crippled from the beatings.

This makes Tien give in to anger, driving him to fight through the guards with feral violence, but Bhuti ultimately defeats him by throwing a spear through his chest.

As he falls dying, Tien remembers Bua's teachings, and suddenly the entire battle and Pim's death are revealed to be all an illusion.

Beginning life anew, the final scene shows Tien, Pim and the remaining villagers bowing before the Ong Bak.