If you liked those primary sources littered throughout Moon Over Manifest, you have Ned to thank. A bunch of them were his letters to Jinx from while he was away at war—and they're the main way we get to know him, as he goes from upbeat and confident to miserable and hopeless.
In terms of biography, Ned is Miss Sadie's son, adopted by the Gillen family in Manifest. Oh, and he's Jinx's best friend. He's always felt bad about not knowing where he came from, and because of that, he's easily tipped over the edge by Lance Devlin's taunts. To prove he's as much of a man and a proud citizen as Lance, he joins the army, too. And sadly, that's where he dies.
Mrs. Larkin is the president of the Manifest Chapter of the Daughters of the American Revolution, so it's no surprise that she's interested in people's family history. Unfortunately, it's to the point of being totally prejudiced against people with unknown backgrounds—like Ned and Miss Sadie.
She's wealthy and influential in Manifest, and is friends with the jerky Arthur Devlin. Until he makes the mistake of dissing her late husband, that is. Then the claws come out, and she helps the townspeople trick him into losing the land he needs to buy for his mine. Nice one.
Lettie and Ruthanne are cousins, and they're Abilene's new Manifest friends. They are totally psyched about the hunt for the Rattler and love hearing Abilene tell them the latest installment of Miss Sadie's stories. They're probably the nicest girls in town, too (apart from Abilene, obvs)—they're the only ones who made an effort to make her feel welcome when she first arrived, running all over town collecting bottles to sell so they could bring her a Coke and a sandwich and get to know her.
Of course, they have a trouble-making side, too. It's their idea to set off fireworks to distract the janitor so Abilene can escape from the school building unnoticed. Sneaky.
Worst. Bosses. Ever.
Arthur Devlin is the owner of the Manifest coal mine, and Lester Burton is his pit boss. They're both corrupt as corrupt can be, and mean, to boot. They're both proud members of the Ku Klux Klan, and pride themselves on keeping their workers poor and downtrodden.
Sweetest. Lady. Ever.
Hattie Mae has written the News Auxiliary column for the Manifest Herald since she graduated from high school in 1918, and she's still in the newspaper business. She acts like a doting aunt towards Abilene and eventually lets her take over her column.
Mr. Underhill, the undertaker, tries to stop the girls from discovering who the Rattler is. Well, he tries to stop their spy hunt at least. The thing is, he doesn't want them finding out about his own shady past. As he finally admits to Hattie Mae, he was the one who leaked information to Devlin and Burton and the sheriff during the town quarantine.
Sheriff Dean is corrupt as they come. He only lets Shady keep his whiskey still because he wants his own share of the liquor. Which ends up being all of it, since he's got the power in town. But even he isn't all bad. When his brother-in-law comes to town to hang Jinx, he helps protect the boy. Not because he likes Jinx, though—just because he doesn't like his brother-in-law bossing him around.
Sister Redempta is the one person who Abilene recognizes immediately as not a universal. She's a teacher in Manifest and also a midwife. And she's the only one in town who befriended Miss Sadie and knew that Ned was Miss Sadie's son. Her compassion in keeping Miss Sadie updated on Ned's well-being was what kept our "fortune-teller" going all those years.
Oh, and of course, Sister Redempta turns out to be—you guessed it—the Rattler.
Judge Carlson is the only official in Manifest who isn't under Devlin's influence. When he rules in favor of the townspeople being able to buy the late Widow Cane's land, he does it all by the book. They got it fair and square. And Devlin was just outta luck.
Finn is Jinx's uncle, but he's sure ain't a very nice one. He uses Jinx as his mole in the audience when he does his cons, and he puts the thought in Jinx's head that he's cursed. He dies—in the act of trying to kill Jinx—because he's frightened by the Rattler, and falls over into an animal trap and hits his head. Not to be mean, but he kind of got what was coming to him.