Where had Stoker been when he wrote these letters? In the study of his home in… Kensington? Yes, that’s right, Stoker was living in Kensington in 1900. Harold remembered from Conan Doyle’s diary-that is, in one of the volumes that hadn’t been lost-about how Stoker had had his house outfitted for electric lights in that year; it had been one of the first private houses in London to have them. Conan Doyle talked about the shocking experience he encountered each time he’d visit Bram under those electric bulbs. Harold held the plastic sheets up very close to his face, communing with the pen strokes. What did they say?

Everything, Harold soon learned, and yet nothing at the same time. He and Sarah divided up the letters from the fall of 1900, trying to find any written to Conan Doyle. They found short letters to Stoker’s entire extended family, they found obsequious letters to every well-known theater professional in London, and they even found repentant letters to the writer Hall Caine, to whom it seemed that Stoker owed a considerable sum of money. But they found none written to Conan Doyle, except the carbon-copy receipt of a single telegram Stoker had sent. On December 1, 1900, Stoker had sent a telegram to Conan Doyle that read, in its entirety, “Come at once. Please. B.S.”

It was equal parts thrilling and infuriating. What did Stoker need to see Conan Doyle about so urgently? Where was Conan Doyle’s reply? What were those two up to, after all?

Harold felt sure that Stoker held the key to everything that was happening, but he couldn’t think of what Stoker and Conan Doyle had gotten into together. His first thought was that they had composed a story together, and yet that failed to explain any of the mystery surrounding Cale’s final clue. Why not just make that story public, however poor it might have been?

Harold tried to imagine Stoker’s involvement in Conan Doyle’s other known activities at the time. Had Stoker joined him in one of his brief, unsuccessful investigations for Scotland Yard? None of the newspaper reports at the time mentioned anything about Conan Doyle having discovered anything particularly noteworthy. Scholars had even checked the Scotland Yard records, which were quite thorough. Whatever Conan Doyle had gotten up to there, it hadn’t amounted to much.

Curiously, Harold did find a letter in one of the piles addressed to one “Inspector Miller, Scotland Yard.” Bram had written him a brief note thanking him for his assistance. “Your kind help at Newgate was very much appreciated,” read the letter. Harold thought this odd but didn’t know quite what to make of it. Why would Stoker have been writing to Scotland Yard? And Newgate… Did that mean someone had been in prison?

After an hour of poring over the semi-legible letters, most of Harold’s excitement had faded. In all the letters Bram Stoker had written in the fall of 1900, and into the winter of 1900-1901, there was nothing addressed to Conan Doyle and nothing that seemed like it could have sent Alex Cale into a depressive stupor.

“Nothing, right?” said Sarah as she set down a handful of letters.

“Right. Nothing.” Harold wasn’t sure what to do next.

“That’s about it for these boxes.”

Harold could do nothing but nod. There was something here, he was sure of it. But where? He turned the words of Alex Cale’s final message over and over in his head. Then he spoke them aloud.

“ ‘ The old centuries… have powers of their own… ’ ” He let the Dracula quote drip from his lips. “The old centuries…” It was a beautiful phrase, Harold thought. “… ‘Which mere modernity cannot kill.’ ” How poignant and poetic that last bit was as well-“mere modernity.” There are some things, some evil things, so old that not even a little thing like modernity can stomp them out.

“What was Cale trying to tell us about Stoker? Why was he pointing us to Stoker’s letters? What did Stoker know that Cale discov…” Harold trailed off midword. The flash of inspiration in his head was sudden and discrete. It was like the moment he’d had in the hotel armchair. There had been a period of not-knowing, and then this moment, and now Harold had entered a period of knowing. He simply knew.

“The diary is gone.” As Harold spoke the words, their truth became even more manifest.

“What do you mean?”

“The diary is gone. Destroyed. That’s got to be it. What other news would have upset Cale so much? Remember, in the hotel, he didn’t have the diary. In his two flats, he didn’t have the diary. In the suicide note we found in the British Library, he didn’t even say he had the diary, only that he knew what had happened to it.”

“So what happened to it?” Sarah asked.

“It’s gone. There never was a diary to find.”

“I don’t understand. Everyone agrees that Conan Doyle had written the diary, right? He’d written dozens of other volumes of the thing.”

“Yes. Conan Doyle wrote it. But then it was destroyed.”

“Why would he have destroyed it?”

“He didn’t.”

“Then who did?”

Harold smiled and gestured to the letters at their feet. “Bram Stoker.”

Sarah made a sour face. This news was not making her happy. But Harold was exhilarated. The thrill of inspiration overtook him, the pleasure of a problem solved. As Harold’s face brightened, Sarah’s darkened in equal measure.

“How did Cale know that?” she said.

“It must be in the letters. But not these letters. Later ones. Do you get it? Conan Doyle wrote the diary. Bram Stoker stole it, or threw it out, or something like that. And then he and Conan Doyle must have exchanged letters about it. That’s how Cale knew. ‘Mere modernity’ didn’t destroy Conan Doyle’s old diary. Bram Stoker did.”

Harold was up in a flash, ringing the bell for the library attendant to come back. He hurriedly asked her for the volume of letters chronologically after the ones they were currently looking at. She made him fill out a new request form, which he did impatiently. His own handwriting became quickly more smudged and illegible than even Stoker’s.

It was an agonizing fifteen minutes for Harold while the attendant was off to fetch the letters, and he and Sarah were forced to wait in the rare-manuscript room. He paced back and forth maniacally, hands behind him. When he looked over at Sarah, he found her lost in her own thoughts. Yet something on her face-some shadow of concern and disappointment-gave him the impression that her thoughts were very different from his own. He couldn’t imagine what she was feeling, and he didn’t know how to ask.

Finally the attendant returned with another box, tied with the same white string.

It was less than five minutes before Harold found what he was looking for, though it felt a lot longer to him. His sweaty fingers slipped across the smooth plastic as he shuffled through the pages. “Dear Arthur,” began the letter he held. “Your anger is understandable, but unfounded. Anything I have done-no, everything that I have done- has been done in the spirit of friendship and goodwill that exists between men such as you and I. If you will not thank me now, then I trust that one day you will thank me from the gates of heaven, when St. Peter alone whispers the truth from his lips. Let us discuss this in person, shall we? I can call on you anytime you like. B.S.”

The next letter in the stack continued the argument.

“Dear Arthur,” it read. “These bitter insults do not become you. But there is no reason for us to exclaim our opposite views in these missives. Let us sit in your study with a bottle of brandy, as we have so many times before, and hash out this affair. B.S.”

The third letter conveyed even more anger and ill will between the men than the first two.

“Dear Arthur,” read the third letter. “Please stop this childish behavior. I’m afraid that what you want from me I cannot give. It’s been burnt in your own fireplace, from the first ‘elementary’ to the bitter end. And your rude and unseemly letters have been burnt up in mine. Please, I beg of you, let me come to your house and discuss this matter with you. Allow me the chance to explain myself, and I will allow you the same chance as well. B.S.”