The abhorsen is an inherited role which involves the fighting of necromancers, the Dead and Free Magic constructs. It is an often a hard and tiring job and leaves most abhorsens looking aged beyond their years. It can be inferred that abhorsens usually die of their job, ie: getting killed by a Free Magic Construct or necromancer, etc. and often the next abhorsen is quite young, taking on the role in their late teens.
The Abhorsen Trilogy mainly takes place in the Old Kingdom, a place which is rife with Charter and Free Magic. Ancelstierre which is the neighbouring country is based on 1920's version of England or perhaps, Australia. There are two types of magic in the Old Kingdom: Charter Magic, which is constrained and proper magic, the 'good' magic in a sense. The other one is Free Magic, 'bad' magic in a sense. It is wild and unchannelled and dangerous to both the user and the target of that magic.
Another important part of the Abhorsen trilogy is the bloodlines. There are 3 bloodlines in the Old Kingdom. The Abhorsen as previously explained, the Clayr, which are characterised as a group of mainly women (there are very few male Clayr) who alway sport blonde hair, a genetic tan and the amazing yet burdensome gift of the Sight- the ability to see into the possible futures. The last bloodline is the Royal family and the only ones that can make and bind Charter stones. They obviously rule over the Old Kingdom and it was once believed that the Royal Family died out due to the betrayal of one of it's princes, Prince Rogir, who fell to necromancy and Free Magic. However, this was proved wrong with the discovery of Rogir's half-brother, Toriggan aka Touchstone's frozen body in Holehallow. Holehallow, the traditional burial place of the Royal Family. This discovery had taken 200 years after Rogir's betrayal.
The story of the two Abhorsens, Sabriel and Lirael is very well constructed and intricate in it's design. Sabriel and Lirael are half-sisters. Sabriel being the older of two by 18 years. Sabriel was raised mainly in the country of Ancelstierre as part of a plan to defeat Rogir, who by this time was a creature of the Dead and now known as Kerrigor. Lirael was illegitmately conceived as part of another plan to defeat another evil in the Old Kingdom. Lirael's mother was Arielle, a Daughter of the Clayr and her father was Abhorsen Terciel. Arielle had seen through her Sight what she specifically must do to preserve the Old Kingdom- that was conceiving Lirael. She was a very powerful conduit of the Charter magic thanks to such a strange and powerful genetic heritage. She also had one companion, the Disreuptable Dog, which has been a very popular character with fans.