A Victory for Kregen(1980)
(Book 22 in the Dray Prescot series)
A novel by Alan Burt Akers (Kenneth Bulmer)
The ending of Prescot's stark adventures as a living chess piece in the city of blood games was to be as terrifying as the perils that had gone before. Because now that transposed Earthman had to fight his way back to his embattled Vallian homeland across a sky full of danger and a sea full of death. And when he returned - if he could - he would find the combat joined, his son at doom's door, his troops up against superior odds, and a battle he must personally fight that would be two battles in two different places at the same time!
Used availability for Kenneth Bulmer's A Victory for Kregen
April 1980 : USA Mass Market Paperback
July 2007 : USA, Canada, UK Kindle edition