Poul Anderson 
Dancer from Atlantis [EPUB ebook] 

AN ACCIDENT IN TIME…Duncan Reid was snatched out of the twentieth century from a cruise liner in the mid-Pacific. Oleg Vladimirovitch came from Novgorod in medieval Russia. Udin was a Hun barbarian who lived by cunning and the axe. Erissa had been a sacred priestess in a lost continent. And a mistake in a time-experiment by a race from the far future had thrown these four unlikely comrades together, pulling them through a warp in the fabric of space and time to a world which was ancient history.The strange alliance that Duncan and his comrades formed in that unfamiliar world was to take on a significance that none of them could have foreseen. For not only their own future, but they very future of the world they had found was at stake…