Time warp from 21st century to 16th Samurai Japan. Bloody battles. Young Japanese/American woman buys a kimono and is involved with daimyo.
Mari is a 34 year old woman, trapped in an unhappy marriage, buys an antique kimono and is warped back to 16th century Japan, where she is commanded by a magician/wizard Yamabushi daimyo. He is a warlord and is embroiled with the reigning shogun to gather troops to put down a rebellion of peasants. He is very old....being rather immortal, and has retainers of Yamabushi cult, and a particularly nasty tengu advisor who is a shapeshifter.
Mari is involved in all of this and rarely escapes back to the 21st century, but then she decides that as weird as Japan in the 16th century is, it's a more exciting life than married to her data communications husband, Steven.
Mari returns a couple of times to modern Kyoto, but the lure of Lord Mori makes her put the kimono back on and in the light of the full moon, she is transported back to his castle. She is able to research the particular battle that is historical, and she knows the ending. Back she goes and they (Lord Mori and his advisors) have usage for her knowledge: Who wins this battle?