Gateway, by Sharon Shinn

Gateway, by Sharon Shinn
Young Adult/Adult, 2009

From fantasticfiction.co.uk:
As a Chinese adoptee in St. Louis, teenage Daiyu often feels out of place. When an elderly Asian jewelry seller at a street fair shows her a black jade ring - and tells her that 'black jade' translates to 'Daiyu' - she buys it as a talisman of her heritage. But it's more than that; it's magic. It takes Daiyu through a gateway into a version of St. Louis much like 19th century China. Almost immediately she is recruited as a spy, which means hours of training in manners and niceties and sleight of hand. It also means stealing time to be with handsome Kalen, who is in on the plan. There's only one problem. Once her task is done, she must go back to St. Louis and leave him behind forever. . . .
Trackgeek: While some of the travel between worlds bit can be rather confusing, but overall Sharon Shinn did a good job of managing the whole different worlds (iterations) part and coming up with a good explanation. Also, the love story, while a little instaneous to begin with, develops nicely throughout the book as Daiyu really has to evaluate what she is doing in another world as she tries not to forget her old world and the important things that she learned about life there.
Grade: B+