The Family Trade
Charles Stross
 Miriam's adoptive mother gives her a shoebox filled with items that belonged to Miriam's birth mother, a Jane Doe who died mysteriously when Miriam was only a baby. Among other items, Miriam finds a locket. Inside is a design not unlike a Celtic knot, and when she focuses on it, she is transported to a parallel world that never developed beyond the Dark Ages—except for the men on horses who try to kill her with machine guns. Miriam quickly finds herself caught up in the feuds of her estranged family, which calls itself the Clan. The Clan has used the genetic ability to travel back and forth between the two worlds to build a lucrative import/export trade. However, one of their main sources of income is transporting drugs into and out of the United States which bothers Miriam for ethical and other reasons. Miriam finds a kindred soul in Roland, a distant relation who would also like to be free of the Clan's machinations.