The Revenant Pact — Megan Miller

Princess Josceline de Vetisi helps her father reign over a lost citadel. The world outside is saturated with a corruption that sinks into everything it touches and makes it impossible for the city to spread out more than one hundred and fifty miles away from the magical tree that protects it.

With so many people in such a small place and no way out, tensions in Drasule run high every day. But Josceline loves her people, and when dead and missing citizens begin to turn up in a brain-washed state, she knows it is up to her and to her bodyguard, the illusionist Raniero, to find who is responsible and set it right.