The place of no stars - Erin Hunter (Warriors: The broken code #5)

Goodreads 4.4

The time has come to enter the Dark Forest.

ThunderClan's deputy, Squirrelflight, has vanished with the cat now known to be an impostor, and suspicion and mistrust now reign among the five Clans. They now know the cause of their ancestors’ mysterious silence—as well as the terrifying truth of the danger they must face if they hope to bring light back to the darkness...