Allegiances are shifting among the Clans of the warrior cats who roam the Forest. With tensions so delicately balanced, former friends can become enemies overnight, and some cats are willing to betray their own Clan. Fireheart is more determined than ever to uncover the truth about Tigerclaw, though it isn't easy. However, at the same time, Fireheart has to carry on his warrior duties and cover for Graystripe, whose affair with Silverstream is in full heat. But, everything changes when he finds out she's pregnant with Graystripe's kits. This is where everything changes in Thunderclan. Fireheart and Graystripe face danger with Tigerclaw, who has noticed Graystripe missing many times. But then tragedy strikes when Silverstream's kits come early and she dies a painful death while giving birth to them. Graystripe, the father of the kits and mate of Silverstream, is left heartbroken. The whole of ThunderClan now knows about his affair and it seems like Graystripe will never be trusted again. Later, a band of rogues led by Tigerclaw attack ThunderClan's camp. During the chaos, Tigerclaw corners Bluestar in her den and tries to kill her. Fireheart arrives just in time to save his leader and drive Tigerclaw away. Bluestar is very shaken and unable to believe Tigerclaw's mutiny, though she manages to announce Tigerclaw's exile from the Clan. Fireheart then reveals Tigerclaw's treachery to all of ThunderClan. Tigerclaw then, one by one, asks the warriors Darkstripe, Longtail and even Dustpelt if they want to join him but each cat refuses. Then after a very long wait by Bluestar, Fireheart himself is made deputy, but this announcement is made after moonhigh, which is against Clan tradition. Life is harder and things change at full speed. Fireheart is unsure if he will ever be a good deputy but he is sure that he hasn't seen the last of Tigerclaw. Meanwhile something strange is going on about two RiverClan cats that seem to be linked to ThunderClan. At the end of the book, Graystripe decides to join RiverClan, along with his and Silverstream's kits to raise them. Fireheart tries to make him reconsider his choice, but this later proves to be unsuccessful. He is left heartbroken as he recalls all the adventures that he and Graystripe had been through together, and thinks about how lonely he will be with his best friend gone forever. Fireheart then returns to the ThunderClan camp as their new appointed Clan deputy