A boy and a girl fall in love, that much is always the same.
And even though love doesn't often get this far in stories, they soon become married -- Nai Maak and Nang Naak, both knowing they'll be husband and wife forever. Unfortunately, the king is fighting a war and Nai Maak is conscripted to serve in it, love notwithstanding. So, as a dutiful citizen he leaves his village and his new (And newly with child!) bride behind, promising to come back the first opportunity he gets.
Nang Naak's love stays strong, never faltering; she steadfastly waits for Maak to come back, but her baby comes to term before he is able to. Hers is a backwater village without any medical care, though, and when the childbirth goes wrong she dies. Her passing, and the portentous circumstances of it, are deeply mourned by the village, but nobody knows where Maak is to tell him, so he never learns what happened. Even after she is buried, her love and strong spirit refuse to perish, still waiting for Maak's return.
Eventually, not that much later, he does return. It is night, and the village is silent, so he goes to his house. There, on the porch, the ghost of Nang Naak waits for him looking exactly the same as she did in life. He's so happy to see her and his infant son that he doesn't leave his house or talk to anybody in the village for the next few days.
Despite all of the ghost's work to keep him convinced, he starts seeing things that shouldn't be there. Once, upon return from the forest, he glimpses her arm stretched from the porch of the stilted house all the way to the ground, a good two or three meters. Confused, unsure about what he really saw, Maak doesn't ask her about it. Later that night, as she's sleeping, he wakes and looks over to see her face and body glistening white with ten thousand maggots. Much as anybody else would, he gets the hell out of dodge.
Love is a funny thing, though, and Nang Naak's ghost is enraged that he left her so quickly and brutally. The ghost pursues him wherever he goes, gruesomely killing anybody who tries to help Nai Maak, anybody who tries to stop her. Not knowing what else to do, Maak enters the temple at Mahabute, where the monks tell the ghost she may not come. Defying them, she enters the monastery at night to be with him at last.
Among the monks is a talented novice visiting from a monastery far away. He sees Nang Naak's ghost enter, and manages to surprise her and capture her in a ceramic pot, which he sinks to the bottom of the river. Indebted to the monastery, Nai Naak becomes a monk there, and stays until his passing.
A universally known Thai tale of love and revenge from beyond the grave. This story is told to every Thai child who needs a reminder not to misbehave, and a candle is lit for Nang Naak by every young man who wants to escape conscription. Her shrine is near Bangkok, and attracts visitors from far and near to give incense, flowers, and prayer to her spirit. These offerings are said to bring fortune and protection to anybody who has no other hope. The tale is so ubiquitous in the culture of Thailand that over twenty movies have been made out of it, every single one a box-office hit. One of those movies is the third most-seen ever in Thailand, right behind Titanic and Jurassic Park.
Whether Nang Naak really existed is still up for debate. However, it's agreed that her story was first told sometime in the nineteenth century, and that at least some parts of it probably happened. That makes her folklore a truly living tradition, considering that most spirits and practices go back before Thailand had any written history. She is assumed to have lived in the reign of either King Rama III (1841-1851), Rama IV (1851-1868), or Rama V (1868-1910) -- in any case a very recent life on the time scale of the past.