Fire and Ice (Warriors: The Prophecy Begins #2) by Erin Hunter

FIRE ALONE CAN SAVE OUR CLAN

Fireheart is now a ThunderClan warrior, but danger still lurks in the forest. The cats of RiverClan are growing restless, while WindClan is weak and facing threats from all sides. As tensions build to an explosive climax, Fireheart faces not only imminent battle, but betrayal from within his own Clan.