Ranger's Apprentice The Royal Ranger Ambush at Sorato by John Flanagan
Will and Maddie are in Toscana on a diplomatic mission when word comes of a cavalry force crossing the northern body and marauding through the countryside.
At the behest of the emperor, the rangers head north to investigate. They discover that the invaders are a group of Temujai—a reconnaissance force searching for a place to penetrate and invade. So Will and Maddie must split up to gather forces and information in order to push the Temujai back once again.
As the Temujai move their forces ahead, cutting at the Toscan forces, Maddie and Will must step up and lead their allies to victory, despite the danger of one of their greatest enemies.