They don’t exactly look like a coven—Amelia Atwater-Rhodes and her three friends, locking arms as they walk, their voices overlapping and merging into giggles. It’s a fine Friday morning in Concord, Massachusetts, whose tiny historic center—the green, the white wooden Unitarian church, a salmon-colored Colonial house on the slope of the old British graveyard—still bears a pleasing resemblance to the black-and-white reproductions of its earlier incarnations, posted around town.

The Colonial house is also a landmark of a different kind. “That's Risika’s house!” Amelia says, pointing to it. Boxes are visible through the windows; someone seems to be moving in. But when Amelia was writing her newly published novel, “In the Forests of the Night,” only Risika, her three-hundred-year-old teen-age vampire-protagonist, inhabited it. From the house, Risika could see both the graveyard and the church, which she had attended when she was Rachel, a mortal eighteen-year-old who changed into a vampire in 1702. “Forests” has another teen-age Concord character—Jessaca—who writes what she believes is fiction about vampires, though most vampires regard her creativity as eavesdropping, and her novel as an expose. In Amelia’s forthcoming novel, “Demon in My View,” which will appear next spring, Jessaca publishes her book, and as the vampires read about the details of their lives they begin making plans to “dice the writer into bite-size bits.”

Climbing the hill to the graveyard, Amelia and her friends gab about Aubrey, Caryn, and Sarah—other shapeshifting vampires, witches, and vampire-hunters who populate one or another of Amelia’s novels. It’s a conversation they’ve been having for years—now spiked by gibes about mortal Concord Carlisle High School sophomores, who are sometimes reincarnated in Amelia's writing, complete with fangs.

Amelia is a polite, serious fifteen-year-old with an air of quiet composure. She’s the acknowled...