Throughout the novel, secrets take many forms. They both unite and divide characters. This trope is introduced early on, when Frankie shares with Zeke that she is writing a Nancy Drew fan-fiction novel. She feels the novel is weird and strange and thus has kept its existence a secret. Telling Zeke about the novel and asking him to read it indicates the trust Frankie feels for him. Later, she shares the novel with her mother (who shares it with Hobart)—further evidence that Frankie not only trusts her mother but has gained confidence in her unique identity. The novel’s publication and success demonstrate that secrets are not always meant to be kept.

The novel’s most important secret is the poster itself. Zeke and Frankie agree that they must not reveal its authorship. Both are adamant that this secret must be kept forever, giving them control over their art but also affording them protection; they recognize that they might be ridiculed for its strangeness and thus regarded as societal outcasts. However, neither of them anticipates the ways in which the poster will take on a life of its own. As the poster gains notice and is regarded by some as evidence of a dark or satanic presence in Coalfield, Frankie and Zeke become increasingly certain that revealing their authorship would have negative repercussions.