A Princess Of Roumania (White Tyger Book 1) by Paul Park
Teenage Miranda mopes about her small Massachusetts town, feeling insecure because she was adopted long ago from a Romanian orphanage. She has one friend, brash Andromeda, and hopes to make another out of shy Peter (who is missing his right arm due to a birth defect and mourning his dead mother who taught him poetry).
But vast forces are at work, and secret agents have been planted in her town. Miranda, Andromeda, and Peter drift together one night to chat with other teenagers (or so they think) next to a bonfire. Suddenly they are thrown into an alternate-reality version of the early twentieth century.
Here, Romania and Germany are superpowers, Britain has been destroyed by a tidal wave, and America is a backwater teeming with “savages” of British descent. Africa is a hotbed of rising technology. Even so, magic abounds, and Miranda is a missing princess.
Andromeda, though, has been turned into a dog (and still gets a viewpoint)! Peter inexplicably has his missing right arm replaced with a full-grown man’s arm. They must piece together what has happened, but get separated almost immediately!
The villains in particular are compelling: the pitiable yet power-mad sociopath Nicola Ceausecu, and the evil German elector. Powerful, creepy, and recommended.