Starlight (Warriors)

Starlight is the fourth book in the second series of "Warriors", called "Warriors: The New Prophecy". The book is told from three different points of view: Leafpool and Squirrelflight, two sisters, and Squirrelflight's love interest, Brambleclaw.
This book takes place in a forest around a fictional lake. The forest is populated by groups of feral cats, who live in groups that call themselves Clans. The four Clans are ThunderClan, ShadowClan, WindClan, and RiverClan. The cats usually train to become warriors, who hunt and fight for their Clans.
Plot.
Leafpool.
Leafpool has to care for ThunderClan with her teacher, Cinderpelt. She and Cinderpelt are medicine cats, meaning that they heal the cats of their Clan. She finds a place called the Moonpool, where the Clans can contact the spirits of their ancestors. She eventually falls in love with a WindClan warrior called Crowfeather (which is forbidden, as Leafpool and Crowfeather are from different Clans). Leafpool also discovers that Brambleclaw has started to train with Tigerstar and Hawkfrost, his evil father and brother, in dreams. She wonders if he is truly loyal to ThunderClan.
Squirrelflight.
Squirrelflight discovers a place where ThunderClan can live. She begins to struggle with her emotions for two male cats, Brambleclaw and Ashfur. She likes Ashfur more for a while when she finds out that Brambleclaw has been training with evil cats. She wonders if Brambleclaw is loyal to ThunderClan. Eventually, though, she decides that she loves Brambleclaw, and chooses him over Ashfur.
Brambleclaw.
Brambleclaw starts dreaming of a place called the Dark Forest, a place where the spirits of evil Clan cats go when they die. In those dreams, he trains with Tigerstar and Hawkfrost, his evil father and brother.