A Seneca telling
This retelling follows tale 26 in Arthur C. Parker's Seneca Myths and Folk Tales (1923), 'The Horned Serpent Runs Away with a Girl Who is Rescued by the Thunderer'. It is one Seneca version of a story shape told across the Northeast and Great Lakes: the sky powers against the powers of the deep waters. Details differ from teller to teller.
Two suitors
The Thunderer, Hi'non, often hovered about a certain village, hoping to win a young woman there, and he hated all evil beings and watched for them at their work. One night he found that another suitor was visiting her: a graceful young man in a fine suit of clothing that shone as if freshly washed, with a black stripe of porcupine quills down the back, a long neck, and small, bright eyes. The stranger asked her to come away with him, and she promised to go in three days.
The lodge beneath the lake
On the third night she went with him. He led her over the hills to the high rocky shore of a lake, took her by the waist, climbed down the cliff, and dived with her into the water. They came to a dim lodge full of fine things, and there they were married. Her husband urged her to choose a new dress from the many hanging in the lodge, but each smelled of fish, and she hesitated. Looking more closely, she understood that the garments were the skins of great serpents.
The Thunderer's arrow
She fled, forcing her way up through the water to the surface on a stormy night. Behind her came a monstrous serpent with blazing eyes and horns on its head, and in the flash of lightning she saw that its eyes were her husband's. As it coiled to seize her on the slippery rocks, there was a peal of thunder and a blinding flash, and the serpent fell dead, struck by one of Hi'non's arrows. A strong arm caught her and carried her home to her father's lodge.
Purification
The Thunderer told her she must be purified, and in the women's sweat lodge she was freed of the serpent's young, which the Thunderer killed as they fled. He then showed the people that the serpent's power could be contained, so that it could no longer harm them.