The Reckoners by Doranna Durgin is currently 99c at Book View Cafe
http://bookviewcafe.com/bookstore/book/the-reckoners/
Your choice of DRM free mobi or epub, previously published by Tor although this version is apparently the authors cut so may be somewhat different.
There are a number of other specials also to be found at
http://bookviewcafe.com/bookstore/category/specials/
The Reckoners: A powerful ghostbuster raised by a spirit, her brilliantly eccentric backup team, a cat who isn’t a cat at all…and a fiercely driven bounty hunter from a different dimension who brings them together when worlds collide.