Maura thought of that faceless swirl of black that she had glimpsed in O’Donnell’s bedroom last night, and a chill prickled the back of her neck. She didn’t believe in Satan. But she did believe in evil. And last night, I was surely in its presence. Her gaze fell on Oliver’s sketch of the horned goat. “This thing-this Azazel-is he also a symbol of the Devil?”

“No,” said Oliver. “Azazel is often used as a symbol for the Watchers.”

“Who are these watchers you keep talking about?” asked Frost.

Edwina looked at Maura. “Do you have a Bible, Dr. Isles?”

Maura frowned at her. “Yes.”

“Could you get it for us?”

Maura crossed to the bookcase and scanned the top shelf for the familiar worn cover. It had been her father’s Bible, and Maura had not opened it in years. She took it down and handed it to Edwina, who riffled through the pages, setting off a puff of dust.

“Here it is. Genesis, chapter six. Verses one and two: ‘And it came to pass, when men began to multiply on the face of the earth, and daughters were born unto them, that the sons of God saw the daughters of men that they were fair; and they took them wives of all which they chose.’”

“The sons of God?” asked Frost.

“That passage almost certainly refers to angels,” explained Edwina. “It says that angels lusted after earthly women, so they married them. A marriage between the divine and the mortal.” She looked down at the Bible again. “And here’s verse four: ‘There were giants on the earth in these days; and also after that, when the sons of God came in unto the daughters of men, and they bore children to them, the same became mighty men which were of old, men of renown.’” Edwina closed the book.

“What does all that mean?” asked Frost.

“It says that they had children,” said Edwina. “That’s the one place in the Bible where these children are mentioned. These offspring resulted from matings between humans and angels. They were a mixed race of demons called the Nephilim.”

“Also known as the Watchers,” said Sansone.

“You’ll find references to them in other sources that predate the Bible. In the Book of Enoch. In the Book of Jubilees. They’re described as monsters, spawned by fallen angels who had intercourse with human women. The result was a secret race of hybrids that supposedly still walks among us. These creatures are said to have unusual charm and talent, unusual beauty. Often very tall, very charismatic. But they’re demons nonetheless, and they serve the darkness.”

“You people actually believe this?” asked Jane.

“I’m just telling you what’s in holy writings, Detective. The ancients believed mankind was not alone on this earth, that others came before us and that some people today still carry the bloodline of those monsters.”

“But you called them the children of angels.”

“Fallen angels. Flawed and evil.”

“So these things, these Watchers, are like mutants,” said Frost, “hybrids.”

Edwina looked at him. “A subspecies. Violent and predatory. The rest of us are merely prey.”

“It’s written that when Armageddon arrives,” said Oliver, “when the world as we know it ends, the Antichrist himself will be one of the Nephilim. A Watcher.”

And their mark is on my door. Maura stared at the sketch of the goat’s head. Was that symbol intended as a warning?

Or an invitation?

“Well,” said Jane, and she looked pointedly at her watch. “This has been a really valuable use of our time.”

“You still don’t see the significance, do you?” said Sansone.

“It makes for a great story around the campfire, but it doesn’t get me any closer to our killer.”

“It gets you into his head. It tells us what he believes.”

“Angels and goat demons. Right. Or maybe our perp just likes to play head games with cops. So he makes us waste our time chasing after ocher and seashells.” Jane rose to her feet. “The crime scene unit should be here any minute. Maybe you people could all go home now, so we can do our jobs.”

“Wait,” Sansone cut in. “What was that you just said about seashells?”

Jane ignored him and looked at Frost. “Can you call CSU and find out what’s taking them so long?”

“Detective Rizzoli,” said Sansone, “tell us about the seashells.”

“You seem to have your own sources. Why don’t you ask them?”

“This could be very important. Why don’t you just save us the effort and tell us?”

“First, you tell me. What’s the significance of a seashell?”

“What kind of shell? A bivalve, a cone?”

“Does it make a difference?”

“Yes.”

Jane paused. “It’s sort of a spiral. A cone, I guess.”

“It was left at a death scene?”

“You might say that.”

“Describe the shell.”

“Look, there’s nothing special about it. The guy I spoke to says it’s a common species found all over the Mediterranean.” She paused as her cell phone rang. “Excuse me,” she said, and walked out of the room. For a moment no one said anything. The three members of the Mephisto Foundation looked at one another.

“Well,” Edwina said softly, “I’d say this just about clinches it.”

“Clinches what?” said Frost.

“The seashell,” said Oliver, “is on Anthony’s family crest.”

Sansone rose from his chair and crossed to the window. There he stood gazing out at the street, his broad back framed in black by the window. “The symbols were drawn in red ocher, mined from Cyprus,” he said. “Do you know the significance of that, Detective Frost?”

“We have no idea,” Frost admitted.

“This killer isn’t playing games with the police. He’s playing games with me. With the Mephisto Foundation.” He turned to face them, but the morning glare made his expression impossible to read. “On Christmas Eve, he kills a woman and leaves satanic symbols at the scene-the candles, the ocher circle. But the single most significant thing he does that night is place a phone call to Joyce O’Donnell, a member of our foundation. That was the tug on our sleeve. It was meant to get our attention.”

“Your attention? It seems to me this has always been about O’Donnell.”

“Then Eve Kassovitz was killed in my garden. On a night we were meeting.”

“It’s also the night O’Donnell was your dinner guest. She was the one he stalked, the one he had his eye on.”

“I would have agreed with you last night. All the signs, up till then, pointed to Joyce as the target. But these symbols on Maura’s door tell us the killer hasn’t completed his work. He’s still hunting.”

“He knows about us, Anthony,” said Edwina. “He’s cutting down our circle. Joyce was the first. The question is, who’s next?”

Sansone looked at Maura. “I’m afraid he thinks you’re one of us.”

“But I’m not,” she said. “I don’t want anything to do with your group delusion.”

“Doc?” said Jane. Maura had not heard her come back into the room. Jane was standing in the doorway, holding her cell phone. “Can you come into the kitchen? We need to talk in private.”

Maura rose and followed her up the hallway. “What is it?” she asked as they stepped into the kitchen.

“Could you arrange to take the day off tomorrow? Because you and I need to go out of town tonight. I’m going home to pack an overnight bag. I’ll be back to pick you up around noon.”

“Are you telling me I should run and hide? Just because someone’s written on my door?”

“This has nothing to do with your door. I just got a call from a cop out in upstate New York. Last night they found a woman’s body. It’s clearly a homicide.”

“Why should a murder in New York concern us?”

“She’s missing her left hand.”