The third book in the Merchant Princes series.
Miriam Beckstein, is a tech journalist in Boston, who discovered in the first book that she was born in a parallel world, and that she and some of her relatives hold a rare gene that allows them to step between worlds. In her feudal home world, her relatives have become merchant princes, wielding enormous power over the local economy.
Miriam, thoroughly American, doesn’t fit in well in that other world, and resents becoming a pawn in her family’s dynastic games. Meanwhile, back on our Earth, the U.S. government has become aware of the Family and considers them dangerous narco-terrorists.
Very entertaining, but best read in sequence after the first two books.