Guerreiros de Alavana de N.M. Browne, publicado em 2011? De Google Livros :
A mist envelops a school group in the year 2000 and, on the other side, Dan and Ursula find themselves in what looks like the year 75 AD. They come to understand that they have been called through time to battle for the Combrogi, a Celtic tribe nearly wiped out by the bloodthirsty Romans. While becoming Combrogi warriors, Dan and Ursula realize that they have strengths and powers never imagined and they learn to depend on each other and their tribesmen as they battle for the future of Britain.