The Royal Ranger: The Red Fox Clan: Ranger's Apprentice

Red Fox Clan is the first in a two part sequence about a group of rebels trying to take over the kingdom. It also is the second book in the "Royal Ranger" sequence, and one of the later books in the Ranger's Apprentice series. Maddie has now completed most of her ranger training and is returning home to the castle for a short visit. While there, she explores some secret tunnels. We also learn of the "Red Fox Clan" - a group of country bumpkins that think that dynastic succession should only be through the male line. (Maddie and her mother Casandra are female heirs to the throne.) Horrace leads a small group to quash the rebellion. However, they find the army they are chasing is much larger than expected. Maddie sneaks out and discovers the true red foxes as well as their leader.
The story ends on a cliffhanger with the kingdom in balance. The next book picks up right where this left off. The author really enjoys writing from the perspective of youthful characters. His female characters are strong, yet able to put on "dainty" charm when needed.