This novel is based on the life of one of the 19th century's first and most significant fossil hunters. Mary Anning (1799–1847) was an uneducated working-class woman, living on the edge of poverty in a culture in which social standing, wealth, education, and gender set the boundaries of a strict caste system. All this worked against her receiving the kind of acknowledgment and acclaim that she deserved. She discovered plesiosaurs, ichthyosaurs, and other fossils that turned early-19th-century assumptions inside out. Not only did she find and excavate the fossils, she recognized them as being different from any living creatures or previously discovered fossils. This was an era when the Church of England was still steadfastly sticking to Bishop Ussher's proclamation that the world was created in 4004 BC. Such a short history implied that the world and the organisms in it had changed very little or not at all from their forms at the beginning. These fossils, and others like them, led British scientists to examine seriously the concepts of extinction, evolution, and the ancient geological history of Earth.

Lamarck and a few other European naturalists had already suggested that fossil shells of snails, clams, oysters, and other invertebrates were different from presently living species. But those differences required a well-trained eye and close observation to recognize. Mary Anning's fossils were huge, spectacularly different from any living creature, and had jaws filled with terrifying teeth. These "sea monsters" caught the attention of trained naturalists and the general public in ways that small mollusk shells never could.

A middle-class spinster, Elizabeth Philpot –who was sent away with two of her sisters to live in Lyme Regis when their brother inherited the family property and married –developed an interest in fish fossils and became Mary's fossil-hunting partner and her champion to the scientific community. Mary's talent for discovering specimens, in the fossil-rich cliffs and outcroppings along the beaches between Charmouth and Lyme Regis on the south coast of England, drew scientists and amateurs to her, but without bringing the recognition she richly deserved. Instead, some of Mary's new acquaintances hoped for financial reward by buying specimens cheaply from her, then reselling them at a profit. Others recognized the scientific importance of the finds and sought to publicize them, but without naming Mary as the true discoverer. Several recent books and articles have begun to rectify this lack of recognition.

In the present book, the opening chapters are told from the viewpoint of Elizabeth Philpot. But as she becomes acquainted with Mary Anning, more and more of the narrative reflects Mary's view of what is happening. Alternating chapters tell the story in Elizabeth's words and then in Mary's. Georges Cuvier, William Buckland, Charles Lyell, and several other famous figures from early-19th-century science make cameo appearances, but most of the action is along the beach, in the fossil-bearing strata. Chevalier's novel captures these characters as well as the muted excitement of the fossil beds.

This is a work of fiction, with dialogue and descriptions of the thoughts and emotions of the characters as imagined by the author. However, it appears that the narrative follows rather closely the actual history of Mary and Elizabeth's groundbreaking (literally) work and its reception by the scientific establishment of the time. Besides the drama and suspense of the narrative, students will get quite an accurate image of the two women's contributions, as well as a sense of the confusion, anger, jealousy, and excitement that their discoveries triggered in the fields of geology, paleontology, and biology at that time. Mary and Elizabeth's friendship was sometimes strained. Elizabeth's family looked down on working-class Mary and thought that she was encouraging Elizabeth to act in undignified and unladylike ways – walking around on muddy beaches, picking up strange rocks. Mary's family thought Elizabeth was putting uppity ideas in Mary's head, causing her to forget the financial value of her fossil hunting – in their opinion, the only significance the specimens possessed. Chevalier's writing also evokes the atmosphere of a small, out-of-the-way village (Lyme Regis) as one of its less-respected citizens is suddenly the object of attention from rich and famous visitors. In an unusual feature for a novel, the book ends with a brief bibliography and suggestions for further reading.

By the way, fossils are still being discovered in those beach-side cliffs where Elizabeth and Mary searched so carefully. Two centuries of continued erosion and careful excavation have moved the exposed faces back beyond the main strata where the women found the remains of the giant marine reptiles. But even casual day-tripping visitors can still find dozens of fossil ammonites, belemnites, and other marine invertebrates imbedded in the cliff faces and fallen rocks. A word of caution: if you go, watch the tides. At high tide, almost all the beach is flooded, and it is easy to get trapped against the cliff face with the incoming tide. The sea is often rough, and trying to wade or swim to safety is not a good idea. Also, the steep cliffs sometimes collapse, burying anything (and anyone) on the beach below. Mary Anning herself was almost killed in a landslide on the beach; her beloved dog died in the accident. Fortunately, Mary survived to continue her remarkable series of discoveries, as described in the present book. In 2010, belated recognition finally came to Mary Anning, when the Royal Society of London named her to their list of the 10 women in British history who have had the most influence on science.