An ancient artifact of evil is found by chance and enters the world. A young woman named Angharad, who is "Summerborn" i.e. a witch, learns that it is her mission to track down this artifact (a puzzle-box) and face its evil at the risk of great danger to herself, lest all magic be destroyed by its great evil. Her task is complicated by the fact that the general public in her pseudo-medieval world are severely prejudiced against witches, and sometimes lynch them - or worse.
With the help of a young boy, a wizard, and an alcoholic veteran - and the more ambiguous association of an enigmatic assassin - she sets out on this quest.
This book is not up to DeLint's usual standards. It's overwhelmingly typical, and overall quite mediocre. It's further compromised by the fact that the first half of the book was rewritten (?) from previously published short stories, which means it just sort of meanders around, and the plot doesn't actually get going until the second half of the book.
Not dreadful, if you're a fan of classic fantasy, but there's much better out there.