A cosmic catastrophe, the Ring of Fire, strands the West Virginia town of Grantville back in time in the middle of the Thirty Years War. One of its ripple effects is that Japan has pulled back from a policy of isolation and staked out its own claims on the west coast of North America. But it is not the only power interested in that part of the New World, and the native Americans have also responded, in different ways, to the unexpected colonists. And there are conflicts among the colonists themselves.

In settling the fate of this part of the New World, a few remarkable individuals have an outsize role to play: Oyamada Isamu, a samurai on his first independent command; Yells-at-Bears, a young native woman of Vancouver Island; Father Blanco, a Jesuit priest and former missionary; and Iroha Data-hime, the daughter of the Grand Governor of New Nippon.