The FBI agent looked first at D’Agosta, then at Margo, his eyes like silver coins in the dim light. “Dr. Green,” he said to Margo. “It is nice to see you again after all this time. I wish it could have been under more pleasant circumstances.”

Margo smiled an acknowledgment.

“I have asked you here,” Pendergast went on, “because it is now a certainty that the two murders we have been investigating as separate affairs are, in fact, linked. Vincent, I have kept certain information from you because I did not want to involve you any more than necessary in my son’s murder investigation. I’ve put you in an awkward enough position with the NYPD already. But now the time has come to share what I know.”

D’Agosta inclined his head. It was true: Pendergast, through no fault of his own, had burdened him with a terrible secret. But that was, as his grandmother used to say, acqua passata, water under the bridge. At least he hoped so.

The agent turned to Margo. “Dr. Green, I know that I can count on your discretion — nevertheless, I must ask you and everyone here to keep what is spoken of within these walls absolutely confidential.”

There were murmurings of agreement.

Pendergast, D’Agosta noticed, seemed uncharacteristically restless, his fingers tapping on the table. Normally he was as motionless as a cat.

“Let us review the facts,” Pendergast began. “Exactly eleven days ago this evening, my son, Alban, was found dead on the doorstep of this house. A piece of turquoise was found in his digestive tract. I traced the turquoise to an obscure mine on the shores of the Salton Sea in California. A few days ago, I visited that mine. An ambush awaited me: I was attacked.”

“Who the hell could get the drop on you?” D’Agosta asked.

“An interesting and as yet unanswered question. As I managed to subdue my attacker, we were both subjected to a paralyzing agent of some kind. I blacked out. Once I regained consciousness, I apprehended my assailant and he was incarcerated. The man has remained absolutely silent, his identity as yet unknown.”

He glanced back at D’Agosta. “Let us now turn to your case: the death of Victor Marsala. The prime suspect appears to be a gentleman who posed as a scientist and examined a curious skeleton in the Museum’s collection. With Margo’s assistance, you were able to determine three additional items of interest. First: a bone was missing from the skeleton.”

“The right femur,” Margo said.

“Evidently our ersatz scientist made off with this bone, for reasons unknown. He later killed Marsala.”

“Perhaps,” said D’Agosta.

“Second: the skeleton in the collection did not match its accession label. Instead of being a young Hottentot male, it was an elderly American woman — most likely the remains of the wife of a Museum curator who was put on trial for killing her in 1889. He was acquitted: there was no body. Now you have found the body.” Pendergast looked around the table. “Have I missed anything of importance so far?”

D’Agosta stirred. “Yeah — just how are these two murders connected?”

“That leads to my third point: the man who attacked me at the Salton Sea, and the man you are searching for in connection with Victor Marsala’s death — this would-be ‘visiting scientist’—are one and the same.”

D’Agosta felt himself go cold. “What?”

“I recognized him immediately from your most excellent composite image.”

“But what’s the connection?”

“What indeed? When we know that, my dear Vincent, we will be well on the way to solving both cases.”

“I’ll have to go interview him in Indio, of course,” D’Agosta said.

“Naturally. Perhaps you’ll be more successful than I was.” Pendergast shifted restlessly and turned to Margo. “And now, perhaps, you could fill in for us the details of your own inquiry?”

“You’ve pretty much covered it,” Margo said. “I have to assume the curator, a man named Padgett, snuck his wife’s corpse into the Museum, macerated it in the Osteology vats, and then placed it in the collections with a false accession record.”

Across the table, Constance Greene had drawn her breath in sharply. All heads turned toward her.

“Constance?” Pendergast asked.

But Constance was looking at Margo. “Did you say a Dr. Padgett?” These were the first words she had spoken since the conference began.

“Yes. Evans Padgett. Why?”

For a moment, Constance did not reply. Then she passed a hand over the lacework at her throat. “I’ve been doing archival research into the background of the Pendergast family,” she said in her deep, strangely antique voice. “I recognize that name. He was one of the first people to publicly accuse Hezekiah Pendergast of peddling a poisonous patent medicine.”

Now it was Pendergast’s turn to appear startled.

D’Agosta was growing increasingly confused. “Wait. Who the heck is Hezekiah Pendergast? I’m totally lost.”

The room fell silent. Constance continued to look at Pendergast. For what seemed like ages, the FBI agent did not respond. Then he gave an almost imperceptible nod. “Please proceed, Constance.”

“Hezekiah Pendergast,” Constance continued, “was the great-great-grandfather of Aloysius — and a first-rate mountebank. He began his career as a snake-oil salesman for traveling medicine shows and, over time, devised his own ‘medicine’: Hezekiah’s Compound Elixir and Glandular Restorative. He was a shrewd marketer, and during the late 1880s sales of the nostrum quickly exploded. The elixir was inhaled — not uncommon in those days — using a special kind of atomizer he called a Hydrokonium. An old-fashioned nebulizer, really, but he patented the device and sold it along with the elixir. Together they helped restore the wealth of the Pendergast family, which at the time had been in decline. As I recall, the elixir was called a ‘pleasant physic for all bilious complaints’ that could ‘make the weak strong and the neurasthenic calm’ and ‘perfume the very air one breathes.’ But as use of Hezekiah’s elixir spread, rumors began to rise: of madness, homicidal violence, and painful, wasting death. Lone voices — such as Dr. Padgett’s — rose in protest, only to be ignored. Some medical doctors decried the elixir’s poisonous effects. But there was no public outcry until an issue of Collier’s magazine exposed the compound as an addictive and lethal blend of chloroform, cocaine, noxious botanicals, and other toxic ingredients. Production ceased around 1905. Ironically, one of the final victims was Hezekiah’s own wife — named Constance Leng Pendergast, but always known to the family as Stanza.”

A freezing silence descended on the room. Pendergast had resumed looking into space, fingers drumming lightly on the table, his expression unreadable.

It was Margo who broke the silence. “One of the newspaper articles we uncovered mentioned that Padgett blamed his wife’s sickness on a patent medicine. When I did the isotope analysis of her bones, I got some anomalous chemical readings.”

D’Agosta glanced at Constance. “So you’re saying that Padgett’s wife was a victim of this patent medicine — this elixir formulated and sold by Pendergast’s ancestor — and that he killed her to end her pain and suffering?”

“That’s my guess.”

Pendergast stood up from his chair. All eyes swiveled toward him. But he simply smoothed his shirtfront and then sat down again, his fingers trembling ever so slightly.

D’Agosta was about to say something, then stopped. A connection among all these facts was starting to assemble itself in his mind — but one so bizarre, so terrible, that he could not bring himself to seriously consider it.

At that moment, the door opened quietly and Mrs. Trask entered. “There’s a call for you, sir,” she told Pendergast.

“Please take a message.”

“Pardon me, but it’s from Indio, California. The man said it can’t wait.”