I'm not entirely sure how I ended up reading this book; all the authors I remember mentioning it are people I associate with sff and this is not speculative, except insofar as all historical fiction is speculative.

Griffith has the gift of the historical fiction writer; she knows how to make the pages come to life and make the book more real than whatever happened. Her version takes over reality.
Not that I knew anything at all about Saint Hilda before reading this book, so it wasn't as though there was much to supplant. But her transformation of the 7th century from that weird time period when no one pays attention to Britain into a fully realized world was fantastic.