These are the books by Garth Nix that are reviewed on this site:
Sabriel must cross into Death to find her father. She can do it with the protection of Charter Magic and the tools of the necromancer, but it is dangerous . . .
'Does the walker choose the path, or the path the walker?' Lirael's destiny is not what she wanted, or expected.
Lirael finds there is a task that needs to be done. It needs to be done by anAbhorsen, and only she can do it.
Arthur's come by a key, by mistake. But now he's got it, he might as well have a go with it. It belongs to the House. A very magical place.