A few other characters make a difference in the Days' lives. First and foremost is Aunt Diane, the "capable" (9.7) one, who brings groceries and sticker books for Patty and the kids when Patty is too busy to do the same (i.e. every day). Diane looked after Libby after the family was killed, but Libby was so maladjusted that she killed Diane's dog after it bit her foot. As this is a story about forgiveness, Diane forgives Libby in the end.
There's also Libby's nosy sister Michelle, ten years old, and the… other sister Debby, seven. We know very little about them, what with them being dead and all.
Other minor characters include Jim Jeffreys, the banker. "I knew almost nothing about Jim Jeffreys, and never asked" (1.6). We don't know anything, either. He's only in one chapter.
The Muehlers are a family who were once friends with Ben, but not since he started hanging out with Satan. Someone with the same name buys the farm in the end—not in the same way that Libby's whole family bought the farm, but, you know, literally. They move into the old Day farmhouse and make it into the home it never was.
In the Kill Club, "Most of the solvers are men. […] Women come for, like, networking. They talk about why they identify with the victims" (3.56). One of those women is Magda, who is "very involved in the effort to free [Libby's] brother" (3.129). She worships Ben and wants him to get out of jail. Another woman who wants Ben freed is Barb Eichel, a journalist who wrote a book about the crime and regrets it because she now believes Ben is innocent.
Bert Nolan is head of the Bert Nolan Home, believe it or not. And Lisette Stephens is a missing girl found dead. Selfish Libby is a little relieved at this. If she were found alive, she might steal Libby's thunder, after all.
Finally, there's Len the Letchy Lender, a loan shark who maybe sleeps with Patty for money. That scene is vague. Len is vague, anyway, the type of person who opens with facts like, "She's got red hair like her mom" (6.35). If Libby knew him, he'd be the type of person Libby would hate, "I hate people who start conversations with facts—what are you supposed to do with that?" (1.87).
Len is arrested in connection with Calvin Diehl. Who's that? He's the killer revealed in the book's final twist. "They think he's like a Kevorkian for people who have bad credit and good life insurance. They call him the Angel of Debt" (3.81). He even "drowned a man in his own wheat" (39.2), an event mentioned in passing early on in the book. Even though all these characters are minor, you don't want to blink during Dark Places, or you might miss little things like that.