The Silver Crown (Book Three of The Guardians of the Flame)

Karl Cullinaine, Walter Slovotsky and several companions leave Home -- the town they've built in this world of dragons and magicians to which they have been transported -- to continue their fight against slavery.  Karl is helped by the faithful and enormous flying dragon Ellegon, with  whom he can communicate telepathically.  Karl is also on a mission to provide protection to the wife and son of a royal family, whose land and castle are under attack by slave-raiding forces.  Fierce fighting and surprises are in store for Karl and his friends, as they fight to defend the kingdom under siege.

The second novel in Joel Rosenberg's bestselling 'Guardians of the Flame' series:

GUARDIANS OF THE FLAME
The Sleeping Dragon (#1)
The Sword and The Chain (#2)
The Silver Crown (#3)
The Heir Apparent (#4)
The Warrior Lives (#5)
Road to Ehvenor (#6)
The Road Home (#7)
Not Exactly the Three Musketeers (#8)
Not Quite Scaramouche (#9)
Not Really the Prisoner of Zenda (#10)