Into the Wild begins with a battle between ThunderClan and RiverClan over Sunningrocks, a strip of land. ThunderClan is outnumbered and their deputy, Redtail, calls a retreat. In ThunderClan territory, the medicine cat, Spottedleaf receives a prophecy from ,StarClan the spirits of their ancestors: "Fire alone can save our Clan." The leader, Bluestar says that it is impossible, because fire is feared by all the cats

Rusty, a house cat, runs into a ThunderClan apprentice, Graypaw, in his backyard. Rusty, however, does not run away, but fights back. Soon Bluestar and Lionheart, Graypaw's mentor, having watched the whole thing, invite Rusty to join ThunderClan. Rusty accepts the next day, but is unwelcomed by most of the Clan. Rusty loses his collar after a fight with Longtail, and Bluestar gives Rusty a new name: Firepaw. He forms a strong bond with Graypaw and Ravenpaw, but Firepaw finds out that Tigerclaw, an ambitious member of the Clan, murdered Redtail, and will stop at nothing to attain his goal of becoming Clan leader. Tigerclaw realizes that Ravenpaw might spill his secret, having watched Tigerclaw kill Redtail, so he plans to kill Ravenpaw. To prevent this from happening, Firepaw and Graypaw lead Ravenpaw to a barn where he would be safe and have company, living with a loner named Barley.

Tigerclaw realizes Firepaw knows his secret, but is still trusted by the Clan. ThunderClan gets in a battle with ShadowClan, and ThunderClan is victorious. Having won because of Firepaw, Bluestar gives him his warrior name, Fireheart, along with making Graypaw a warrior, giving him the name Graystripe.