In this Book Fireheart is now ThunderClan's new deputy, but the previous deputy, Tigerclaw, still haunts Fireheart's dreams. Fireheart wonders if ThunderClan would be ready if Tigerclaw attacked as many of the cats are still shocked about Tigerclaw's disloyalty, and many warriors are badly injured. Bluestar also begins to become distrusful of the Clan after Tigerclaw's betrayal.

One day, Bluestar, accompanied by Fireheart, go to speak with StarClan at Mothermouth, a quarry mine. On the way there, a patrol of WindClan warriors, led by Mudclaw, stop them before Bluestar is able to talk with them. The ThunderClan leader later fears that StarClan sent WindClan to stop them from going to Mothermouth and speaking with StarClan, which causes her to slip into further paranoia.

In the summer months, Fireheart struggles with his disrespectful nephew and apprentice, Cloudpaw, who goes to a Twoleg (human) for food and is one day abducted by them. Fireheart and Sandstorm rescue Cloudpaw, who is found near the barn where Ravenpaw and Barley live. He is accepted back into the Clan, since Fireheart keeps it a secret that Cloudpaw went to humans for food. Fireheart must also deal with the fact that his best friend, Graystripe, is still in love with the dead RiverClan she-cat Silverstream.

Meanwhile, the forest gets hotter and hotter, and a fire sweeps through the forest, destroying ThunderClan's camp and taking the lives of two elders, Patchpelt and Halftail, as well as Yellowfang, ThunderClan's medicine cat. At the end of the book, it was revealed at a Gathering that both Nightstar and Cinderfur have died from a sickness, and that Tigerstar is the new leader of ShadowClan.