The Blue Throne - Chronicles of Cassadon, #3

With the tyrannical warlock King Xerxe now dead, and the threat from Ludova finished, Demelda is left the sole ruler of Vallandria. Inheriting a patriarchal kingdom that has never had a queen is no easy feat, especially when she tries to convince the unstable kingdom that she is capable of leading them to glory. In the midst of facing the troubles in the south, messengers from the north bring worrying news.
A new alliance between Mertova and her mother's kingdom, Predentia, forces Demelda ever closer to the final battle. Her greatest ally, merman Kavic, embarks on a dangerous quest of his own as he sets sail to the treacherous island of Zanzuva to build a bigger army for Queen Demelda. Battling her doubts, and the fiercest of foes, Demelda struggles with the impending fate of an entire realm. Has her vision of a free world been for nothing, or will she find the numbers she needs to finally take her cause to victory?