The Sacrifice the Dead Will Make begins on a ridgetop, just seconds after the end of Book Three, and everything begins to accelerate. Asher becomes more and more fearful of Samantha. Aeternus tightens his grip on Skysill Beach and the eternal ghost’s long-sought prize comes at last into his reach. When Peter’s past is finally revealed, Asher finds he is central to the eternal ghost’s plans, and as Asher’s family, friends, and lovers begin to die, he must become the thing he fears most to save them. To keep the broken Path from ending the world, he’ll offer any sacrifice he has to, even The Sacrifice the Dead Will Make.
Review and read dates are for the whole series; I read it in one go. It really should be one book; the individual books didn't really have any resolved arcs of their own.
I'm increasingly battling with the quality of the writing, but just find the world-building and magic system and plot too interesting. Which makes it very hard to recommend to others, but definitely something I'll finish (jury's out on if I'd ever do a re-read, though).