The story follows the exploits of thirteen-year-old orphan Maria Merryweather (Dakota Blue Richards), whose sole inheritance from her father is a book. This is no ordinary tome, however in Maria's hands, its ancient story comes alive. The book chronicles an age-old rivalry between the Merryweather and De Noir families over a set of magical pearls, and as Maria delves into the mysterious tale, she finds herself fantastically entangled in the bitter feud.
Left penniless by her father's death, Maria has no choice but to leave the city and live with her taciturn uncle, Sir Benjamin Merryweather, at his isolated country estate in Moonacre Valley. On her way to her new home with her caretaker Miss Heliotrope, Maria's carriage is attacked by Robin, the De Noir family's teenaged son. Although she is unharmed, the incident gives Maria a frightening taste of the animosity between the two clans. Having spent the night at her tower, Maria has been surrounded by magic, the stars on the ceiling of her room falls, one by one. She also noticed that the house seemed falling apart. She qestions her uncle, but she was reprimanded not to enter the forest.
When Maria arrives at the Merryweather property, her uncle spies the unusual book in her possession, and immediately confiscates it. With the help of the estate's resourceful chef, however, Maria relocates the book and continues reading, finally discovering the weight of her responsibility: she has been anointed the last Moon Princess of the valley. It is up to her to find the magic pearls before the next full moon and end the conflict between the two families. If she fails in her quest, the dark curse following the Merryweather family will destroy Moonacre Valley for good. But is this a challenge Maria is ready to accept?