First book, but while it has obvious sequel hooks, it stands alone.
The narrator arrives at the place of an alleged haunting -- it's his business -- and discovers that this is one of the real ones. Before he dispels the haunting, he learns that whatever killed the child, creating the ghost, is still hunting for the ghost. He has something new to pursue.
He gets his contacts to attempt to find based on the boy's name, and then goes to ensure his mother is still trapped by his spell. Giving us some of the backstory there. . . .
It involves a familiar consisting of a boy split into three, salt, an obvious trap, something very close to something else, breaking into a jail, a somewhat gruesome piece of necromancy, finding a book that the narrator had dealt with, a volunteer, a childhood hide-out, and more.