Undine
By Friedrich Heinrich Karl La Motte-Fouqué
Cover: Lake Landscape with Ruin by Carl Johan Fahlcrantz · Wikimedia Commons · Public domain
A knight falls in love with a foundling girl who is secretly a water-spirit, and the water makes its claims. Friedrich de la Motte Fouqué's 1811 fairy romance, here in Charlotte Yonge's English, a source for later tales of the sea-maiden.
Summary written with Claude Sonnet 5.5.