Libby is a thirty-one-year-old survivor of a horrific childhood massacre that claimed the lives of her mother and two sisters. She has lived most of her adult life relying on a public donation fund that is now nearly empty. Bitter, isolated, and burdened by severe psychological trauma, she reluctantly agrees to investigate the murders she survived when a true-crime group offers to pay her for information.

Ben is Libby's older brother, currently serving a life sentence for the 1985 murders of his mother and sisters. At age fifteen, he was a secretive, withdrawn teenager whose dark clothing and sullen behavior fueled town rumors of Satanic worship. In the present, he maintains a remarkably calm demeanor in prison, refusing to file an appeal despite claims of his innocence from true-crime enthusiasts.

Diondra is a wealthy teenage girl whom Ben secretly dates in the months leading up to the murders. She is rebellious, heavily uses drugs and alcohol, and flaunts her family's money. Because her parents frequently travel, she operates largely without supervision and draws Ben into her chaotic, risk-taking lifestyle.

Patty is a single mother of four who struggles constantly with severe poverty and a failing family farm. She is deeply stressed by impending bank foreclosures, her children's behavioral issues, and the local rumors surrounding her teenage son. Despite her overwhelming debt and exhaustion, she loves her children and tries desperately to keep her family intact.

Lyle is a young true-crime enthusiast and the treasurer of the "Kill Club," an underground group dedicated to dissecting famous murders. He dresses in a retro 1980s style and genuinely believes Ben is innocent. He serves as Libby's primary contact within the club, funding her investigation and offering companionship as she questions people from her past.

Runner is Patty's ex-husband and the absent father of her four children. He is a gambling addict who abandoned his family, returning only periodically to demand cash from Patty. His reckless lifestyle, drug dealing, and massive debts make him a prime suspect in the eyes of true-crime solvers.

Diane is Patty's older, pragmatic sister who frequently steps in to help manage the Day household amidst Patty's severe financial struggles. Following the murders, Diane briefly served as Libby's guardian before Libby's severe behavioral issues caused a deep rift between them.

Michelle is Libby's ten-year-old sister who is murdered during the 1985 massacre. She is described as bossy and observant, often writing in her diary and keeping close tabs on other people's secrets.

Debby is Libby's nine-year-old sister who also perishes in the massacre. She generally acts as Michelle's loyal assistant in their childhood games, following her older sister's lead.

Krissi is a childhood classmate of Ben who accused him of molesting her as part of a Satanic ritual in 1985. In the present day, she goes by her married name, Krissi Quanto, and works in strip clubs after her life derailed following the media circus surrounding her accusations.

Trey is Diondra's older cousin and a reputed drug dealer, bookie, and Satanist in 1985. He associates with high school dropouts and pressures Ben into reckless activities, including drinking and participating in ritualized animal killings. In the present day, he runs a feed store and claims to have left his dark past behind.

Barb is a former reporter who wrote a sensationalized book about the Day family massacre in 1986. Caught up in the Satanic Panic of the era, her writing heavily influenced public perception of Ben's guilt. She now deeply regrets her involvement and actively believes Ben is innocent.

Magda is a frizzy-haired member of the Kill Club and the leader of the Free Day Society, an advocacy group fighting to get Ben released from prison. She is convinced Libby lied on the stand and aggressively pressures her to officially recant her testimony.

Jim is Libby's grandfatherly fund manager. He bears the difficult task of informing Libby that the public donation fund she has lived on for over a decade is completely depleted.

Len is the loan officer for the bank holding the mortgage on Patty's farm. He frequently delivers bad news about foreclosures and makes inappropriate, predatory advances toward Patty, using her desperate financial situation as leverage.

Peggy is Runner's former girlfriend from 1985. She provided Runner with an alibi for the night of the murders but admits to the Kill Club decades later that she lied to the police.

Calvin is a man who meets Patty in a park prior to the murders, offering to help her with her overwhelming legal and financial troubles. He is a former farmer who understands the devastating impact of agricultural foreclosures.

Crystal is Diondra's daughter who lives with her in a remote, rural area of Missouri. She is highly protective of her mother and deeply invested in the lore surrounding the Day family murders, keeping scrapbooks of old news articles.

Lou is Krissi's father, described as a large, intimidating man. Furious over the molestation allegations involving his daughter, he aggressively searches for Ben on the day before the murders, drawing the suspicion of the true-crime solvers decades later.