Warriors: Into the Wild by Erin Hunter

A housecat joins a wild forest clan, where he must navigate dangerous rivalries and internal treachery to protect his new home . As he trains to become a warrior, he struggles to prove his loyalty while uncovering a murderous conspiracy within the Clan.

This book contains: animal violence, anxiety, bullying, child endangerment, death/grief, deception, divination, gore, and murder/infanticide.