The book opens with Sabriel raising a freshly killed rabbit from death. She is a young girl attending Wyverly College, an all-female boarding school in Ancelstierre. An undead creature enters the dormitory where Sabriel lives and frightens all of the girls. Sabriel, however, notices it is holding a satchel and is attempting to speak. She enters Death to see what it is and notices strings attached to it passing over the waterfall of the First Gate; a sign that the creature is under the control of a necromancer further in Death. It is very weak, but Sabriel makes out that it is a messenger bound by her father who is past the Seventh Gate of Death. She is instructed by her father (through the messenger) that she is to take on the role of Abhorsen and defeat Kerrigor (a powerful Free Magic necromancer) who is attempting to make his way back into Life to break the Charter which binds the Free Magic and thus destroy the Charter of the Old Kingdom. She retrieves the satchel which contains the Abhorsen's bandelier of bells, the Abhorsen's sword and a map of the Old Kingdom.
Having left her school, Sabriel crosses the Wall using papers given to her by her father. Her destination is Abhorsen's House, the home of her father. Near the wall, she meets a southern colonel and his troops. The soldiers are using brute force to stop hordes of Shadow Hands from dismantling the Wall and crossing over. The areas near the Wall are being evacuated and only those who are inhabitants of the Old Kingdom are allowed the cross.
As she continues her journey, Sabriel becomes aware that she is being stalked by a Mordicant, a powerful Dead creature. She is able to outrun the creature and reach the safety of Abhorsen's House, which is located on an island in the center of the river. (The Dead cannot cross fast and deep running water.)
Inside Abhorsen's house, Sabriel is able to rest and obtain food and other supplies, as well as armor. She also meets Mogget, a Free Magic construct who takes the form of a small white cat, wearing a collar with a powerful binding spell on it and a miniature Saraneth hanging from it. Mogget insists on accompanying her on her journey to find her father. Later, they look out over the walls surrounding the house and discover the Dead attempting to build a bridge. Sabriel performs a ritual to summon a flood of water and then flees the house by Paperwing (a magically propelled plane-like structure.) While in the air, Sabriel and Mogget are attacked by the Dead, and Sabriel loosens Mogget's collar to avoid a fatal crash. They fall into a sinkhole, where Mogget, in his unbound form, attempts to murder Sabriel. However, she is able to bind him anew with a ring given to her for that purpose.
The next day, Sabriel and Mogget walk through a tunnel to another sinkhole, which Mogget determines to be Holehallow, the historical burial place of the royal family. Each king is buried in a boat. Sabriel discovers that the figurehead on one of the boats is not a wooden carving but an actual man, who has been imprisoned in that form for two hundred years. The man tells Sabriel that he was a Royal Guard before his imprisonment, and asks to be called Touchstone (a jester's name) for reasons that remain cryptic.
Sabriel, Touchstone, and Mogget continue their journey, stopping to help rid a seaside village of a Dead creature. They obtain a boat there and sail up the coast of the Old Kingdom until they reach Belisaere, the capital. They find the Abhorsen 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 (the sound of which throws everyone who hears it far into the realm of Death) and delay Kerrigor's havoc; and she, to save Touchstone by bringing him (and herself) as far away from Astarael's music as possible. To prevent him from losing to Death, she kisses him roughly in order to keep him focused on Life. 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 (the first of seven necromantic bells that instills sleep and quiescence in those who hear it).