"A year ago, I turned the final page of The Book of the Dead. I don't feel young any more," Sabriel says to Colonel Horyse when they meet for the first time at the border. The title character is tall and slender with ghostly pale skin and raven-black hair. She has been fighting undead creatures since childhood, and her eighteen years weigh heavily on her shoulders. Her burden grows heavier when her father disappears and she realizes his name, "Abhorsen," is a title that has been passed along to her. Like her father, Sabriel is "an uncommon necromancer": she sends the Dead back to Death rather than calling them forth to serve her as most necromancers do. Her journey to find her father shows her curious blend of wisdom and innocence as she takes the prodigious amounts of book learning she has amassed over the years and puts it to practical use. Her situation is learn or die, and she learns quickly, but at no time does she become a larger-than-life heroine who is unbeatable. There is always an element of chance in her battles that could just as easily shift to favor the other side. Her flaws make her more accessible as a character.

The Abhorsen, her father, actually appears only briefly, but readers still get the sense of a man of honor and strongly held convictions who does not abuse his power as a necromancer. He sends Sabriel to school in Ancelstierre to protect her from the Dead creatures he fights, but he faithfully visits with her through a spell on the full moon every month. Sabriel's memories show him as a loving father, and he only drags her into battle as a final resort. He accepts his own death, but he fights to keep his only daughter alive.

Colonel Horyse realizes who Sabriel is almost from the moment they meet. By calling her Abhorsen, he accords her the support and honor her position expects, but he relates to her in a father-daughter manner saying she reminds him of his own daughter who is Sabriel's age. A tough, battle-hardened warrior, Horyse is not surprised by much anymore except the appearance of a teenage girl as defender of the realm.

At her father's home, Sabriel inherits Mogget, a creature appearing to be a large cat wearing a collar saturated with binding spells. The spells force Mogget to serve Sabriel, but it does so at its own pace in its own sly manner. The semblance of a cat bestows a cuddly, domesticated image on what turns out to be a wild creature composed of Free Magic that only wants the Abhorsen dead so it will be freed.

In a hidden valley, Sabriel and Mogget find the funeral barges of the royal family. One figurehead of a nude young man catches Sabriel's eye, but when she examines him closer she feels faint emanations of magic running beneath his wooden frame. The magic leads past the First Gate of Death where she realizes the young man has been trapped half in, half out of Death. Following her gut instincts, she returns him fully to life. The young man claims to have been a member of the Royal Guard, but the only name he is willing to give is "Touchstone," the name commonly given to the fool in folktales. Throughout the novel, he is the stiffest character in actions and demeanor, perhaps as an offshoot of so many years trapped as a wooden man. Only as his feelings for Sabriel bring him back to life does he begin to relax somewhat, but he still carries a burden of guilt as a result of his unwitting betrayal of the royal family he served.

Kerrigor embodies the evil Sabriel fights. He is absolute evil without even a hint of compassion to link him to the humanity he cast aside hundreds of years ago. His quest for power corrupted his soul and made him anathema to the Land of the Living. His goal is to open the Gates of Death and conquer the living.

The primary theme of Sabriel is the quest, or journey. Sabriel undertakes a journey to find her father, and life is a journey towards death. Even though Sabriel has dealt with death and the undead since her birth, when it comes to her own father, she is as much in denial as anyone facing the loss of a loved one. Her quest is not to defeat death per se, because it is a natural part of the life cycle, but to face her own fears of death and loss and, if not conquer, at least learn to accept them.