“Comets were often thought to be holy portents. God’s messengers. When Lucifer, the light-bringer, fell, he streaked through the sky just like a tail of fire, it is said.”

“When will the comet be overhead in New York?”

“October eighth, about midnight,” Will said.

“That’s less than two weeks away.” Evie bit her lip, thinking. “You said that the Brethren is a vanished cult. What happened to them?”

“The entire sect burned to death in 1848.” Dr. Poblocki opened a groaning file drawer overstuffed with papers. “There had been an outbreak of smallpox, you see. Several of the Brethren died from it. Apparently Pastor Algoode became convinced it was a sign of God’s judgment and that they should prepare themselves to bring on Armageddon. No one knows exactly what happened, but they think that Algoode gathered his followers and doused the meetinghouse in kerosene—a jar of it was found in the ruins. The doors were barred. A hunter nearby saw the flames and smoke. He said you could hear prayers and hymns turning to screams.”

Evie shuddered. “How awful. Did no one survive?”

“Not a soul,” he said solemnly. “The town of New Brethren was built in the valley below, about five miles from the original camp on the hill. They say that unquiet spirits still haunt the woods of the original Brethren. They’ve heard terrible sounds and seen lights in the trees up on the mountain. No one ventures there, not even the hunters.”

Evie tried to imagine all those souls locked inside the meetinghouse, singing and praying, the mothers clutching their children while the flames raged. “Burned to death. Why would they do such a thing?”

“Why does anyone do anything? Belief. A belief that they are right and just in their actions. Abraham was willing to sacrifice his son, Isaac, because he believed that God had commanded it. To kill your son is unthinkable. A crime. But if you are acting in the belief that your God, your supreme deity whom you must obey, has demanded it of you, is it still a crime?”

“Yes,” Will said.

Dr. Poblocki smiled. “I know you do not believe, Will. But imagine for a moment that you believe fervently that this is truth. In this framework, your actions are justified. Glorified, even. They are inculpatus—without blame. If this is the case with your killer, then he is on a holy mission, and nothing will stop him from seeing it through.”

“What is this?” Evie asked. She had turned to the last page in the Book of the Brethren, which had been torn out. Only the ripped edges remained.

Dr. Poblocki moved in close and peered over the tops of his glasses, squinting. “Ah. That. I can tell you what it is supposed to be. According to the accounts, the Book of the Brethren contained a spell for trapping the spirit of the Beast in an object—a holy relic of some sort—and then destroying the object, casting the Beast back to hell once the mission of the faithful had been accomplished.”

“I don’t understand,” Evie said.

“It’s like the Arabic jinn, or genie. A spirit or demon can be contained in an object and then destroyed,” Will said. He looked troubled.

“Doesn’t seem like much to hang your hat on,” Evie said. “Not that it matters, since the page is missing.”

“Not just missing, but deliberately torn out,” Dr. Poblocki reminded her.

“But who would do that, and why?”

“It seems someone didn’t want the Beast to be destroyed after all.”

“Georg, may I keep this?” Will said, holding up the book.

“Be my guest. Just promise me you won’t start your own doomsday cult with it.”

Engrossed in the book’s illuminated pages, Will didn’t respond.

“And now, it is high time I joined Mrs. Poblocki for our Sunday repast.” Dr. Poblocki gave Evie’s hand a courtly kiss. “I wish you the best with your investigation. Do keep your uncle in line.”

Outside, it had begun to rain. Will opened the day’s paper and offered half to Evie. They cupped the flimsy sheets over their heads and walked quickly across the lawn toward Broadway.

“If our killer is following the eleven offerings of this Brethren cult, he had to hear about them somehow. Is it possible he’s from that region?” Evie gazed at the vast expanse of city. “Don’t you think? Will? Unc, are you listening to me?”

“Hmm? Yes,” he answered absently. His brow was furrowed and his eyes looked tired. This case was obviously bothering him far more than he’d let on. “A solid observation, Evie.”