Shadow Web by N.M. Browne

Shadow Web takes you into a parallel universe where Germany has won World War 2.

Jess is just your normal teenage girl living in London, hanging out with her friends. But a chance meeting in Waterloo Station with her double (albiet a double dressed in rather old-fashioned clothes) sees Jess hurled into a weird new/old London.

Different rules apply and danger stalks every conversation and interaction Jess has in this strange world. Who can she trust? Who is on the 'right' side? What happened to the other Jessica? And how is she going to get back home to her mother?

I loved it.

For good readers 12+

http://www.nmbrowne.com/nmbrowne_books.html