I can't wait for a sequel! The book supposes that Nantucket Island is transported back into the 13th century, all alone except for a Coast Guard windjammer out on a training mission.
The island characters and Coast Guard are very detailed. Stirling has caught the laconic "Down-Easter" personality very well, reflecting his annual vacations to the Island. He also created a memorable female character in the CoastGuard Captain, Marian Alston, a "black, female, ex-ranker, Southern, lesbian" with a highly developed sense of duty and a wry (mostly internal) sense of humor. Luckily, stranded on the Island are some other very useful characters including a Professor of History who's also a science fiction fan and an astronomer who uses her computer and star charts to figure "when" they are.
Adjusting to the "Event" as they call it, isn't easy but the town sheriff starts getting them motivated to grow their own food and make plans for survival. The Islanders accidentally wipe out most of the proto-Indians in the Boston area with the common cold, journey to England to trade for grain and foil the invasion plans of some war-like immigrants from the mainland of Europe.
Stirling's bio lists his love of history, martial arts and other hobbies and he uses them extensively as background detail.
I hated to get to the end of this book. In fact, I turned back to the first page and started in again. Please, please tell me S. M. Stirling is going to continue the story!!!