It seems that each title in the MiddleGate series get just a little bit better than the last. There is more going on plot wise in Kingdom of Trolls than in the previous books, more that ties this story into the larger story of the Serpent's Chain (including the mystery surrounding the disappearance of Sophie's father).
Kingdom of Troll (and in fact all the MiddleGate books) by Rae Bridgman are a great read for anyone who enjoys fantasy or young adult fiction. While the books are listed for ages 9-12, this is an enjoyable read for adults as well. I would recommend reading the books in order, beginning with The Serpent's Spell. I highly recommend Kingdom of Trolls and the whole MiddleGate series.
Kingdom of Trolls by Rae Bridgman
Published by Sybertooth Inc
Kingdom of Trolls (MiddleGate) by Rae Bridgman is available at Amazon.com