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.

It is a time of peace between the warrior Clans, and all four are thriving. Then Firestar, leader of ThunderClan, discovers a terrible secret: The warrior ancestors of StarClan have lied to him. Firestar must embark on a perilous journey to right their wrong - and nothing will ever be the same again.

As Leafbare approaches, a new danger threatens the Clans. Twoleg construction has encroached on Clan territory, poisoning the stream and making prey especially scarce for SkyClan. Meanwhile, their leader, Leafstar, is struggling with a loss of vision while trying to maintain authority over a Clan that increasingly doubts her ability to lead. In ShadowClan, Tawnypelt senses peril as the Twoleg construction threatens the Moonpool, but she can’t get any cat, especially her son, TigerStar, to listen.

For generations, four Clans of wild cats have shared the forest according to the laws laid down by their ancestors. But the warrior code is threatened, and the ThunderClan cats are in grave danger. The sinister ShadowClan grows stronger every day. Noble warriors are dying - and some deaths are more mysterious than others. In the midst of this turmoil appears an ordinary housecat named Rusty...who may turn out to be the bravest warrior of them all.

Long before Firestar left his kittypet home to join ThunderClan, a band of cats from the mountains set off on a dangerous journey in search of a new home....