Elinor was raised in Ancelstierre, south of the wall that block the magic of the Old Kingdom. Never in her childhood was magic even mentioned.
Terciel was gathered by the current Abhorsen, Tizanael, from the orphanage he has live in since his parents and sister died. He will become the next Abhorsen in Waiting - learning all of the Charter magic needed to keep the dead in death and from coming back to the world to cause trouble.
Their paths cross when a necromancer begins to summon the dead to attack Elinor.
Nix has written this prequel, starring the parents of Sabriel, to the delight of his fans. What started out as the Abhorsen trilogy is one of my favorite fantasy series ever!
Nix, Garth. (2021). Terciel & Elinor. New York: Katherine Tegan Books.