Deep in the heart of the forest, four Clans of warrior cats coexist in uneasy harmony - but uncertain times are upon them, and dangers threaten the precarious balance of the forest. Fireheart is a ThunderClan warrior now, but his troubles are far from over. The cats of rival RiverClan grow restless while WindClan is weak and faces threats from all sides. Now Fireheart faces not only imminent battle but betrayal from within his own Clan.

For many moons, ThunderClan, ShadowClan, RiverClan, and WindClan have lived in peace in their territories around the lake. But now, they must decipher a mysterious prophecy - a message that will send one young medicine cat apprentice on a quest to determine the fate of all the warrior Clans. 

Hollypaw, Jaypaw, and Lionpaw - grandchildren of the great leader Firestar - possess unusual power and talent. But secrets and uncertainty surround them, and a mysterious prophecy hints at trouble to come. The warrior code is in danger, and these three apprentices will need all of their strength to help the Clans survive.

They have always lived by the code—but only change can keep the peace. A new age is dawning on the warrior Clans. Now a new generation of warriors rises—one wrestling with the legacy of his great ancestor Firestar, one seeking to protect her troubled Clan, and one yearning to prove herself as a medicine cat—as leaders from all five Clans agree that the Warrior Code must be reformed.

The fate of all Clanhood hangs in the balance. After killing Harelight and pronouncing himself leader of RiverClan, Splashtail's thirst for power has only grown. Soon his greed threatens the safety of not only RiverClan but all Clans. Yet Splashtail's trickery knows no bounds, and the Clans find themselves in more danger than they could have imagined. Only one thing is certain: They will have to work as one to defeat Splashtail before he tears them apart.