Installment Immortality by Seanan McGuire

Seanan McGuire’s bestselling and Hugo Award-nominated InCryptid series continues with a whirlwind adventure….

After four generations of caring for the Price family, Mary Dunlavy has more than earned a break from the ongoing war with the Covenant of St. George. Instead, what she’s getting is a new employer in the form of the anima mundi, Earth’s living soul made manifest, and a new assignment: to hunt down the Covenant agents on the East Coast and make them stop imprisoning America’s ghosts.
All in a day’s work for a phantom nanny, even one who’d really rather be teaching her youngest charges how to read.
One ghost can’t take on the entire Covenant without backup, which is how she winds up on a road trip with the still-mourning Elsie and the slowly collapsing Arthur, both of whom are reeling in their own way from the loss of their mother. New allies and new enemies await in Worcester, Massachusetts, where the path of the haunting leads.

With the anima mundi demanding results and Mary’s newfound freedom at stake, it’s down to Mary to make sure that everyone gets out of this adventure alive.
It’s been a long afterlife, but Mary Dunlavy’s not ready to be exorcised quite yet.