Inside the kennel-that-moves, everything was dark.
With this line, we realize that the prologue is going to be from quite an unusual viewpoint. And it is - it is the only part of any of the books to feature a non-feline point of view, as we see it through the eyes of the leader of a pack of dogs. These dogs have been taken into the Treecut place for several nights (presumably to guard it from/find possible arsonists, as Fireheart's dream in Rising Storm reveals that the fire was started by young Twolegs). The pack leader has been enlarging a hole under the fence for the past few nights, and tonight it is wide enough for the dogs to escape. They run into the night forest, eager to taste prey.
The actual book begins in the same moment that Rising Storm left off, with Tigerstar as the new ShadowClan leader at the Gathering. The other leaders greet him, unaware of his past, though they dislike the idea of rogues joining the Clan as well. Fireheart speaks for ThunderClan, as Bluestar had refused to come, and after the Gathering he asks Mistyfoot about Graystripe, who says he's doing well.
When they arrive back at camp, Fireheart reports to Bluestar about Tigerstar's leadership. She is furious, forgetting that the other Clans don't know about Tigerstar's treachery, and becomes convinced that StarClan doesn't care about them anymore. She also fears an attack from ShadowClan, especially since ThunderClan is more vulnerable after the fire, but the attack does not come. A few days later, Cinderpelt tells Fireheart she had a strange dream, hearing the words "Pack, pack" and "Kill, kill" in a language that wasn't Cat. Fireheart can't make sense of it, and puts it out of his mind.
Over the next few days, the Clan slowly continues to recover from the fire. Fireheart assesses the apprentices and suggests to Bluestar that they become warriors, but her fear of them and their mentors being possible traitors makes her refuse (except for Cloudpaw, Fireheart's apprentice). Fireheart watches the kits playing, and is unnerved that Bramblekit looks exactly like Tigerstar; Goldenflower notices, and tells Fireheart that she never told her kits about their father, and that she wants Fireheart to be the one to tell them. Brackenfur confides in Fireheart that he's been watching Speckletail's kit Snowkit because he's hoping to be made his mentor, and he has noticed that there is something strange with the kit. Fireheart goes to Cinderpelt about it, and she promises to do so, after making the journey to the Moonstone to become a full medicine cat.
Fireheart and Sandstorm hunt near the Treecut place. They don't find any prey, and if there was any to begin with, it was scared away by Fireheart's sister Princess shouting his name. She explains that she was worried since he hasn't visited her after the fire, but before she can go home, Twolegs arrive, calling out as if they were looking for someone. Afterward, Fireheart and Sandstorm run into Graystripe along the RiverClan border, and he tells them that Crookedstar is near death, and that Tigerstar has begun visiting the camp. Mistyfoot arrives, saying she cannot find Graypool - the elderly she-cat has been confused lately and may have wandered off. Fireheart finds Graypool, but not in time - Tigerstar meets her first. Believing that he's Oakheart, Graypool wonders aloud why he hasn't asked about the ThunderClan kits he gave her to keep moons ago. This is news to Tigerstar, who tries to coax more information out of her, losing patience and snarling in her face, and she falls down the bank. She hits a rock on the way and is killed by the blow. When Fireheart arrives back at camp, Cinderpelt is examining Snowkit, and announces that he's deaf. Bluestar says that he cannot be a warrior, but does not attempt to comfort Speckletail, and Fireheart realizes that it's almost as if she doesn't care.
On a patrol a few days later, Fireheart discovers some scraps of prey and dog scent, and when Whitestorm reports the same thing, they realize that there must be a dog loose in the forest. He reports it to Bluestar, who in her suspicion blames it on WindClan simply because one of the killed prey was a rabbit and because no dog has been loose in the forest before. A yowling interrupts them, and Fireheart races out to see a hawk carrying away Snowkit. Bluestar proclaims that it's a sign from StarClan that they are at war with ThunderClan. In the Clan's stunned silence, Cloudpaw wonders aloud why everyone is so shocked, because StarClan is only a kit tale. This shocks Fireheart, who never realized that Cloudpaw didn't believe in StarClan. Fireheart and Cinderpelt discuss Bluestar's behavior, and Fireheart worries that Bluestar will accuse WindClan at the Gathering.
At the Gathering, there's news in that Leopardstar is the new leader of RiverClan. Graystripe tells Fireheart that she's been planning to get Sunningrocks back. Bluestar speaks next, accusing WindClan of prey theft. After some arguing, the Gathering ends in a hostile mood. Fireheart tries to reason with Bluestar the following morning, but she insists that they will attack WindClan - and that she will lead the attack herself. Fireheart naps and tries to ask Spottedleaf what to do, but she only shows him the WindClan moorland and gives him the cryptic message that "This is where a battle will not be fought, and blood will not be spilled," conveniently failing to mention whether that would happen only if Fireheart takes action, or if he leaves things as they are. Fireheart decides to take matters into his own paws and heads off to visit WindClan. On the way, he discovers Darkstripe taking Bramblekit and Tawnykit to see Tigerstar. He interrupts just before Tigerstar can give a biased account of why he is ShadowClan leader, and brings them back to camp. With the lost time, Fireheart arrives in WindClan territory just before sunset, and they agree to send Ravenpaw to ask Bluestar for a peace talk. The peace talk works; there is no battle. However, Bluestar is now convinced that Fireheart is a traitor. Later in the day, she goes missing, and it turns out that she had gone to visit the Moonstone to challenge StarClan. They warned her of a "pack", but once again, Fireheart has no idea what it could mean.
Half a moon later, RiverClan tries to claim Sunningrocks back, fighting with the dawn patrol. In the heat of battle, fearing for Bluestar's life, Fireheart reveals to Mistyfoot and Stonefur that Bluestar is their mother, but they refuse to accept her. Graystripe warns Fireheart of an attacking Leopardstar, and by that time, ThunderClan reinforcements arrive. RiverClan flees after banishing Graystripe as a traitor. Bluestar decides to make Cloudpaw a warrior. Cloudtail's former denmates are furious that they were not made warriors as well, so they sneak out that night to try and confront whatever's loose in the forest. Swiftpaw and Brightpaw end up going - Swiftpaw is killed and Brightpaw gravely injured. The only thing Brightpaw can say is "Pack, pack, kill, kill", revealing that this "pack" is what did this to her. They do not know if she will die, so Bluestar performs a ceremony where a dying apprentice can be given a warrior name - and names the young cat Lostface as part of her war against StarClan.
The time for apprenticing Bramblepaw and Tawnypaw is coming up, so Fireheart decides upon himself and Brackenfur as their mentors. They tour the territory, and the time finally comes when Fireheart has to answer the young cats' questions about their father. At the next Gathering, Tigerstar requests that his kits be brought to ShadowClan, but Bluestar tells him that she will wait until the next moon.
Not long afterward, Longtail comes to Fireheart and reports that he saw Tigerstar feeding a rabbit to a dog pack living at Snakerocks. At last, the ThunderClanners know what has been in the forest for the last few moons. They set out to confront the dogs the next morning, finding a trail of dead rabbits leading from Snakerocks to the camp and a dead Brindleface outside the camp. They do their best to break the trail, evacuate the Clan to Sunningrocks, and set a line of cats to lead the dogs to the gorge. Fireheart is the last one, and Tigerstar catches him, pinning him down for the dogs to catch him. Bluestar rushes in and saves Fireheart's life, falling into the gorge along with the dogs. Mistyfoot and Stonefur help pull her out of the river, and Bluestar lives long enough to reconcile herself with her kits and promise Fireheart that he will be a great leader before giving up her last life and joining StarClan. Tigerstar runs back to his own territory. Fireheart and Graystripe head back to their Clan.