Edge of Wonder by Jenna Collett

It was a simple plan.
Alice Montgomery has spent her life on the run from the mercenaries killing Wonderland royals. Still years away from claiming her birthright, she follows through on a risky plan to trick them into thinking she’s dead. Unfortunately, it works a little too well, and now she’s trapped, haunting an old clockmaker’s cottage.
Better late than never.
Sebastian Ward could care less about the prophecy that says he’ll aid a princess in reclaiming her throne. He has better things to do, like making a name for himself as a kingdom renowned ghost hunter. Until his latest haunting brings him face to face with a ghost from the past.
With their paths on a collision course, Sebastian is forced to fulfill his part of the prophecy, triggering the mercenaries to continue their hunt, and as they embark on a quest through a ruined kingdom where nothing is what it seems, he’ll have to decide whether guarding the last princess of Wonderland is worth losing the only thing he’s ever wanted: his freedom.