I just finished the (currently) last part of Ben Aaronovitch's PC Peter Grant series. At the end:
Victory (the mother of one of the abducted children) goes out into the woods to replace the just-replaced child with the one that was replaced earlier. Peter steps in, and exchanges himself for both children. Then, out of nowhere, Beverly comes and takes Peter back.
So, yes, it is somewhat confusing, and, it has to be said, relatively unsatisfying as far as endings and explanations go. I understand that Aaronovitch partly wants to keep up an air of mystery about how magic and magical creatures work, partly wants to set up future novels. But still, almost none of the final 2 or so chapters seem to make any sense in themselves:
Where did the second child that was originally replaced come from? Why did the queen want to switch them back now? If the queen wanted to switch them back, why would she sway Victoria to come switch them yet again? What did she even want with those children, given that she apparently did not care at all which human she got in the end? And if any human works, then why the heck is she keeping replacing them? How is this ending any solution, will she not just abduct the next child during the next moon phase?
I have the feeling that I am missing something here, probably because I don't know the fae lore well enough. Maybe somebody can enlighten me?