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.

For the first time, all five warrior Clans have settled into their true homes in the territory around the lake. But when a shockingly harsh leaf-bare season descends on the forest, a new darkness begins to spread - a shadow that threatens a beloved Clan leader, the cats’ connection with their ancestors in StarClan, and the very warrior code by which they live.

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 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.

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.