Esther is the eldest Hawthorn sister, born in December with dark hair and a gregarious personality. She shares her family's task of caring for the willow trees along the River Liss by singing to them. She prefers harps and riddle songs and harbors a deep curiosity about Arcadia, where she once became lost as a child.

Ysabel is the younger of the two Hawthorn sisters, born in summer with bright blonde hair. She has a shy disposition, prefers the flute and murder ballads, and enjoys the attention of human suitors. Unlike her sister, she fears the Modal Lands and the border to Arcadia after becoming lost there in her childhood.

Rin is a shapeshifting Arcadian from the land of Faerie who uses they/them pronouns. Governed by the strict rules of magical grammar, they cannot sing but communicate and flirt through musical instruments, riddles, and physical transformations. Rin finds the human world cold and piercing but possesses a deep affection for Esther.

Samuel Pollard is a human gentleman farmer who owns land neighboring the Hawthorn family in Thistleford. He seeks to court Esther to unite their families and lands. He acts overly gallant and showers the sisters with gifts, masking a controlling, arrogant, and jealous nature beneath his polite demeanor.

Agnes Crow is a human woman who lives in Arcadia and operates a mill on the River Liss. Often regarded as a witch, a title she does not dispute, she possesses a deep understanding of the wild grammar that flows from Faerie. She acts as a benevolent mentor figure, helping those who cross the boundaries between worlds.

Rowan is Agnes Crow's daughter, residing in the magical land of Arcadia. She lives alongside the River Liss and assists her mother with their mill, witnessing the strange grammatical transformations the river brings.