WARRIOR CATS: The Scorned Spirits

Not every cat goes to StarClan when they die.

Some cats manage to anger their ancestors so horribly that they are banished from the peaceful, prey-filled afterlife, doomed to walk a different path for the rest of their dying days. But no cat quite knows exactly where the tormented souls go, nor do any of them particularly care. These cats who broke the code are dead and gone, so what harm can they possibly do to living cats? They are dead, unable to interfere physically with the world of the living...

But they certainly aren't powerless to walk in young cats' dreams.