For her protection, Sabriel attends a boarding school across the Wall from the Old Kingdom where her father, the Abhorsen, has the task of sending evil spirits back into Death. She knows something has happened to her father when his Necromancer's bells are brought to the school by magic, but she's scarcely ready to tackle the Old Kingdom's dangers by herself.
Nix has created a vivid and terrifying world where the only thing more dangerous than magic is the wilful denial that it exists. His conception of Death is powerful and poetic. The Dead Hands and animating spirits are far beyond mere zombies in their menace and Mogget, the Free Magic being that is bound into the form of a small cat, is even stranger.
Fantasy readers who appreciate detailed, believable world-building, unfolding mysteries, and fully developed characters will be glad that this is the first volume of a trilogy. The second book is Lirael: Daughter of the Clayr and the third is titled Abhorsen. They are listed as the Abhorsen trilogy in the catalog, though they are sometimes called the Old Kingdom Chronicles. According to Wikipedia, another book in the series is scheduled for fall publication.
Sabriel and its sequels remind me more of Ursula LeGuin's Earthsea stories or Patricia McKillip's Riddle-master trilogy than any of Nix's other series. As Nix observes, “A fantasy novel should be like an iceberg. The story is the visible ten percent but the reader should feel like there is another ninety per cent under the surface that they can't see: it's not in the story but they know it's there.“
PS: The Clayr have the kind of library many would die to work in. And if you like the series, you'll enjoy the extras on the author's website.