The Brightest Shadow

Authors are friends/at least colleagues, they've both been publishing in the genre roughly since the western author codification of PF ~6-7-odd years ago. They've written back-cover blurbs for each others books before, e.g. see Sarah's quote on The Wrack https://johnbierce.com/books/the-wrack/ and the Editorial Reviews by John for the Brightest Shadow https://www.amazon.com/Brightest-Shadow-Sarah-Lin-ebook/dp/B0856ZMG9Z or Weirkey https://www.amazon.com/dp/B08P7TYG41. AFAIK Sarah has not specifically written anything 'in' the series.