Set in the court of Louis XIV, the story blends historical fiction with elements of fantasy as it follows a young woman who serves as the king's natural philosopher. Tasked with studying a sea creature captured by the king, believed to be a mermaid, she discovers its intelligence and humanity, challenging the prevailing views of her time. As she forms a bond with the creature, she must navigate the treacherous waters of court intrigue and scientific discovery, while confronting ethical dilemmas about the treatment of sentient beings and the pursuit of knowledge at any cost. The novel explores themes of power, gender, and the clash between science and superstition.

In the quaint lobstering town of Mackerel Sky, Maine, local legends and everyday life intertwine. The town's origins trace back to Captain Burrbank, who, captivated by the mermaid Nimuë, settled on the cliffs, sparking a community steeped in myth. Centuries later, the tale of the mermaid and the captain continues to shape the lives of the townsfolk. Myra Kelley, a tough widow, becomes the reluctant guardian of Leo Beale, a troubled youth seeking refuge from his chaotic home life. Meanwhile, Derrick Stowe, a talented pitcher, grapples with his identity, yearning to share his love for poetry and his secret relationship with his father. Manon Perle, known for her intricate quilts depicting the town's legendary past, struggles with her own haunting memories of loss. As the community navigates love, secrets, and the weight of their shared history, they must come together to ensure the town's legacy endures for generations to come.