Of Beginnings and Endings(1989)
(The sixth book in the Castaways in Time series)
A novel by Robert Adams
Thrown back through the centuries to a war-torn Britain and America, Bass Foster and his fellow castaways control kings and countries by wielding weapons from a highly advanced future civilization. But the unsuspecting time travelers have attracted the attention of mysterious, awesomely powerful beings who might bring the world tremendous benefit - or destroy it with terrifying force.
Used availability for Robert Adams's Of Beginnings and Endings
June 2014 : USA Paperback
May 1989 : USA Mass Market Paperback
June 2014 : USA, Canada, UK Kindle edition