Katherine Applegate 
Endling: Book Three: The Only 

Endling #3: The Only is the third book in an epic middle grade animal fantasy series by Katherine Applegate, Newbery Medal-winning and #1 New York Times bestselling author.
Two mighty armies are preparing for war, one led by a murderous great cat and the other by a cruel, power-hungry tyrant. But a third army is quietly growing, an army led by a young girl, an army of peace.
Not so long ago Byx, a dairne, was the timid youngest pup in her family. But since her family were all slaughtered by the cruel Murdano, Byx has had to leave her own kind and finds herself at the forefront of a peaceful army, serving her friend and leader, the young Lady of Nedarra.
Can the courage and heart of these young friends really stand in the way of two great armies? Can peace prevail over war?