The whole of RiverClan is sick with greencough and Sundance and Smokeclaw pull together the medicine cats of every Clan to help fight it despite the Clans' hostilities toward one another—and the boundaries set by the warrior code.

Sundance has agreed to be part of ThunderClan and is training to become a ThunderClan warrior. However, her ideas of a grand and peaceful life are questioned when a battle threatens to rise against ShadowClan. Her courage and compassion are tested, and she finds herself locked into a desperate fight for peace. She knows that she must take on the whole of ShadowClan alone—and win.

Smokeclaw is an energetic warrior full of potential and ambition. Sundance is a compassionate kittypet always helping other cats in need. Stories of Smokeclaw spread into Twolegplace, and Sundance sets out to join ThunderClan. Then ShadowClan attacks, and the two young cats, having very different theories when it comes to battling, are given patrols to lead to fight back their way.