SPOILER ALERT: Plot Revealed
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The novel is set in two neighbouring fictional countries: To the south lies Ancelstierre, which has a technology level and society similar to that of early-20th century England, and to the north lies the Old Kingdom, where magic works and dangerous spirits roam the land — a fact officially denied by the government of Ancelstierre and disbelieved by most of Ancelstierre's inhabitants. (Those who live near the border know the truth of it, especially on days when the wind is blowing out of the Old Kingdom.) These dangerous spirits range from undead corpses known as Dead Hands to supernatural beings known as Free Magic elementals.
These living Dead are raised by Necromancers, or black magicians, who roam the Old Kingdom or live in Death, using Hands to do their bidding. To remedy the problem of dangerous, living dead, there is always a sorcerer with the title of Abhorsen, who is essentially a Necromancer himself (or herself), only in the reverse; he puts the dead to rest. At the time of Sabriel, it is her father, Terciel, who has the job of controlling the endless dead creatures doing evil deeds around the Wall, especially difficult since a new evil seems to be rising.
When the current Abhorsen is overcome by one such evil, he sends his bells and sword to his daughter Sabriel, who is being raised in an Ancelstierre school, out of reach of those who might try to strike at her father through her. She must return to the Old Kingdom to rescue her father and prevent the evil's return.
Sabriel is joined on her journey back to the Old Kingdom by an ancient Free Magic construct of unknown origin named Mogget. Mogget appears in the form of a white cat and is bound by a red Charter magic collar to serve the Abhorsen. Sabriel is told never to release Mogget's collar. Sabriel and Mogget take a craft known as a Paperwing to try to find her father. On the way, they are attacked by the Dead. The craft is wrecked, and in order to save herself, Sabriel releases Mogget. The cat reveals himself to be an incredibly powerful Free Magic elemental. It almost kills Sabriel, but she rebinds him with a ring she received from him a few hours before for just such a purpose.
Sabriel and Mogget then find themselves in the pit of Holehallow, the burial place of ancient royalty, where they come across and free their next companion, the mysterious Touchstone, who has been magically imprisoned as a wooden ship's figurehead for over two hundred years. He claims that he doesn't remember his past, or even his own name. At Mogget's suggestion, he asks to be called Touchstone, even though it is a jester's name, because he secretly remembers his failure to protect his family.
The three of them trek through the Old Kingdom in an attempt to find the Abhorsen. They find him in an underground reservoir in Belisaere, trapped in Death. Since he has stayed too long in Death, he cannot return for long, but with what little time he has left, the Abhorsen tells Sabriel about the evil known as Kerrigor. Kerrigor has risen far from Death and intends to wreak havoc in the Old Kingdom and Ancelstierre. Sabriel releases her father from Death, and once they emerge from Death, father and daughter part for the last time — he, to ring the bell Astarael and delay Kerrigor's havoc; and she, to save Touchstone by bringing him (and herself) as far away from Astarael's music as possible. In the process of ringing Astarael, Sabriel's father releases Mogget.
They succeed, but as long as Kerrigor's body is intact, he will rise from Death again and again. Sabriel and Touchstone use another Paperwing to bring them as close to the Wall as possible, and cross over to Ancelstierre to find Kerrigor's body, following the clairvoyant guidance of the Clayr twins Sanar and Ryelle. They find the body, and Sabriel finally defeats Kerrigor by binding him with Ranna and Mogget's collar.
She dies but the previous Abhorsens prevent her from crossing into Final Death as she cannot die without someone else to take her place as Abhorsen. She wakes up with Touchstone before her, and both Mogget and Kerrigor asleep, bound by Ranna.