The castle in Cassiopeia - Michael D Resnick

A crisis has arisen. On their first mission as a team, Pretorius and his Dead Enders kidnapped the real General Michkag and substituted a clone who had been raised and trained in the Democracy. But now they find that the clone likes being the most powerful man in the hundred-world Traanskei Coalititon-and having been raised on Earth, he knows how humans think and react.

This becomes a many-layered problem for Pretorius and what is left of his Dead Enders. As the only humans on a totally militarized alien world, they must first find where the best-guarded member of the enemy's military - Michkag - is hiding and how many aliens, or regiments, or divisions, are guarding him, and then they must find a way past all his lines of defense to kill or capture him.