The beneficial and destructive nature of belief is a prominent theme throughout the novel. Shade’s colony believes in a bat god named Nocturna; they think that she created all bats. Frieda believes that one day Nocturna’s Promise will allow them to live in the sunlight again. This faith in the Promise gives the bats who believe in it hope, and this hope gives them a reason to keep going, despite their oppression at the hands of the much-larger, violent owls.

At the abandoned house, the colony of banded bats’ beliefs are detrimental to their survival. They believe that the Promise involves the banded bats transforming into humans. Shade thinks this belief is uncanny and weird, especially because it causes the house bats to do strange things. Their chanting and the leader bat’s eerie trick seem to keep the house colony in a delusional daze, where they are helplessly vulnerable to Goth’s attack. Instead of giving them a realizable hope, their belief and obsession with their version of the Promise ultimately gets them killed.

Goth’s belief in Zotz fuels his egocentric and violent tendencies. He believes that Zotz made him a strong cannibal, and he thinks it’s a gift that allows him to absorb the strength of the creatures he eats.