“Wait a minute!” Henry stopped at the foot of the stairs. His voice echoed back from several directions. “You mean we’re underground in a cemetery? Like where the bodies are buried?”

“It’s not like that,” she said. “This is the New York Marble Cemetery. All the people here are interred in underground vaults made of solid white Tuckahoe marble.”

“Wow,” Brianna said, “even the cemeteries in New York are strange.”

“Well, there’s a lot of history here. After the yellow fever epidemic in 1822, which took the life of my older sister, Mary Claire”—Molly paused briefly to utter a blessing—“the city banned traditional earth burials south of Canal Street. Later, they extended the ban, first to Fourteenth Street and then all the way to Eighty-Sixth Street. But they still allowed burials in private family vaults like these.”

“Is your sister buried here?” asked Brianna.

“No. We were very poor and couldn’t afford a private burial. And so many people were dying from the fever.” Molly dabbed the corners of her eyes with a handkerchief. “Poor Mary Claire joined the thousands that were buried in a potter’s field that is now called Washington Square Park.”

An ethereal voice sounded from next to Henry. “Oh, how I love hearing a true historian,” it said.

“Ahh!” Henry ducked and ran, tripped, and sprawled into a damp, slimy wall. “Who’s there? Who was that?” He looked all around, but couldn’t find the source of the voice.

“Don’t worry,” Molly whispered softly in Henry’s ear. “Most of them are friendly.”

“Most of who … ?”

“What are you babbling on about?” Coralis hissed.

“Oh, it’s just an unexpected visit from John,” Molly said lightly.

“Wh-h-ho’s John?” Henry stuttered.

“He’s a dentist and a mean one!” snapped Coralis. “And he loves to pull children’s teeth. Now can we stop this incessant chatter and get moving? There are urgent matters to attend to!”

“Coralis, please! You’re scaring them. Do you want them to be afraid of all spirits?” Molly pleaded.

“Nonsense,” he said dismissively. “John Greenwood! Show yourself.”

A fuzzy apparition materialized between Molly and Coralis, gradually taking the shape of a middle-aged man in a finely tailored suit. His eyes were downcast, as if he had just received a scolding from a teacher. “I didn’t mean to frighten anyone. You know how I love guests, and it’s been so long since any children visited.”

A tiny squeal of alarm peeped out from Henry’s pocket as Brianna shivered.

“Henry, Brianna, meet John Greenwood, dentist to George Washington,” Molly announced.

“G-G-G-eorge Washington … as in the first president?” Henry asked.