Halloween is not so spooky in New Zealand, largely on account of the bright, perky evenings and the fact that pumpkin’s not really in season. Here are some book suggestions to fill the void:
The teen blog slightly random-ish list of quality fiction about horror and ghosts.
Some zombie books that are a little bit gruesome.
A list of good Halloween reads from The Horn Book (if the picture books don’t interest you so much, look further down for an excellent selection).
An updated list of recommendations from allhallowsread.com.
Or you can read up about Halloween at history.com.