The American told me that even after Conan Doyle died Holmes continued to loom over his descendants. “Dame Jean thought that Sherlock Holmes was the family curse,” he said. Like her father, he said, she had tried to draw attention to his other works but was constantly forced to tend to the detective’s thousands of fans—many of whom sent letters addressed to Holmes, requesting his help in solving real crimes. In a 1935 essay entitled “Sherlock Holmes the God,” G. K. Chesterton observed of Sherlockians, “It is getting beyond a joke. The hobby is hardening into a delusion.”

  Several actors who played Holmes were also haunted by him, the American said. In a 1956 autobiography, “In and Out of Character,” Basil Rathbone, who played the detective in more than a dozen films, complained that because of his portrayal of Holmes his renown for other parts, including Oscar-nominated ones, was “sinking into oblivion.” The public conflated him with his most famous character, which the studio and audience demanded he play again and again, until by the end he, too, lamented that he “could not kill Mr. Holmes.” Another actor, Jeremy Brett, had a breakdown while playing the detective and was eventually admitted to a psychiatric ward, where he was said to have cried out, “Damn you, Holmes!”

  At one point, the American showed me a thick book, which he had brought to the pub. It was part of a multivolume history that he was writing on the Baker Street Irregulars and Sherlockian scholarship. He had started the project in 1988. “I thought if I searched pretty assiduously I’d find enough material to do a single hundred-and-fifty-page volume,” he said. “I’ve now done five volumes of more than fifteen hundred pages, and I’ve only gotten up to 1950.” He added, “It’s been a slippery slope into madness and obsession.”

  As he spoke of his fascination with Holmes, he recalled one of the last times he had seen Green, three years earlier, at a symposium at the University of Minnesota. Green had given a lecture on “The Hound of the Baskervilles.” “It was a multimedia presentation about the origins of the novel, and it was just dazzling,” the American said. He repeated the word “dazzling” several times (“It’s the only word to describe it”), and as he sat up in his chair and his eyes brightened I realized that I was talking not to Green’s Moriarty but to his soul mate. Then, catching himself, he reminded me that he had a full-time job and a family. “The danger is if you have nothing else in your life but Sherlock Holmes,” he said.

  In 1988, Richard Green made a pilgrimage to Reichenbach Falls to see where his childhood hero had nearly met his demise. Conan Doyle himself had visited the site in 1893, and Green wanted to repeat the author’s journey. Standing at the edge of the falls, Green stared at the chasm below, where, as Watson noted after he called out, “My only answer was my own voice reverberating in a rolling echo from the cliffs around me.”

  By the mid-nineteen-nineties, Green knew that he would not have access to the Conan Doyle archive until Dame Jean died—presuming that she bequeathed the papers to the British Library. In the meantime, he continued researching his biography, which, he concluded, would require no less than three volumes: the first would cover Conan Doyle’s childhood; the second, the arc of his literary career; the third, his descent into a kind of madness.

  Relying on public documents, Green outlined this last stage, which began after Conan Doyle started using his powers of observation to solve real-world mysteries. In 1906, Conan Doyle took up the case of George Edalji, a half-Parsi Indian living near Birmingham, who faced seven years of hard labor for allegedly mutilating his neighbors’ cattle during the night. Conan Doyle suspected that Edalji had been tagged as a criminal merely because of his ethnicity, and he assumed the role of detective. Upon meeting his client, he noticed that the young man was holding a newspaper inches from his face.

  “Aren’t you astigmatic?” Conan Doyle asked.

  “Yes,” Edalji admitted.

  Conan Doyle called in an ophthalmologist, who confirmed that Edalji’s malady was so severe that he was unable to see properly even with glasses. Conan Doyle then trekked to the scene of the crime, traversing a maze of railroad tracks and hedges. “I, a strong and active man, in broad daylight, found it a hard matter to pass,” he later wrote. Indeed, he contended, it would have been impossible for a nearly blind person to make the journey and then slaughter an animal in the pitch black of night. A tribunal soon concurred, and The New York Times declared, “CONAN DOYLE SOLVES A NEW DREYFUS CASE.”

  Conan Doyle even helped in solving the case of a serial killer, after he spotted newspaper accounts in which two women had died in the same bizarre manner: the victims were recent brides, who had “accidentally” drowned in their bathtubs. Conan Doyle informed Scotland Yard of his theory, telling the inspector, in an echo of Holmes, “No time is to be lost”; the killer, dubbed “the Bluebeard of the Bath,” was subsequently caught and convicted in a sensational trial.

  Around 1914, Conan Doyle tried to apply his rational powers to the most important matter of his day—the logic of launching the First World War. He was convinced that the war was not simply about entangling alliances and a dead archduke; it was a sensible way to restore the codes of honor and moral purpose that he had celebrated in his historical novels. That year, he unleashed a spate of propaganda, declaring, “Fear not, for our sword will not be broken, nor shall it ever drop from our hands.” In the Holmes story “His Last Bow,” which is set in 1914, the detective tells Watson that after the “storm has cleared” a “cleaner, better, stronger land will lie in the sunshine.”

  Though Conan Doyle was too old to fight, many of his relatives heeded his call “to arms,” including his son Kingsley. The glorious battle Conan Doyle envisioned, however, became a cataclysm. The products of scientific reason—machines and engineering and electronics—were transformed into agents of destruction. Conan Doyle visited the battlefield by the Somme, where tens of thousands of British soldiers died, and where he later reported seeing a soldier “drenched crimson from head to foot, with two great glazed eyes looking upwards through a mask of blood.” In 1918, a chastened Conan Doyle realized that the conflict was “evidently preventable.” By that time, ten million people had perished, including Kingsley, who died from battle wounds and influenza.

  After the war, Conan Doyle wrote a handful of Holmes stories, yet the field of detective fiction was changing. The all-knowing detective gradually gave way to the hardboiled dick, who acted more on instinct and gin than on reason. In “The Simple Art of Murder,” Raymond Chandler, while admiring Conan Doyle, dismissed the tradition of the “grim logician” and his “exhausting concatenation of insignificant clues,” which now seemed like an absurdity.

  Meanwhile, in his own life, Conan Doyle seemed to abandon reason altogether. As one of Green’s colleagues in the Baker Street Irregulars, Daniel Stashower, relates in a 1999 book, “Teller of Tales: The Life of Arthur Conan Doyle,” the creator of Holmes began to believe in ghosts. He attended séances and received messages from the dead through “the power of automatic writing,” a method akin to that of the Ouija board. During one session, Conan Doyle, who had once considered the belief in life after death as “a delusion,” claimed that his dead younger brother said, “It is so grand to be in touch like this.”

  One day, Conan Doyle heard a voice in the séance room. As he later described the scene in a letter to a friend:

  I said, “Is that you, boy?”

  He said in a very intense whisper and a tone all his own, “Father!” and then after a pause, “Forgive me!”

  I said, “There was never anything to forgive. You were the best son a man ever had.” A strong hand descended on my head which was slowly pressed forward, and I felt a kiss just above my brow.

  “Are you happy?” I cried.

  There was a pause and then very gently, “I am so happy.”

  The creator of Sherlock Holmes had become the St. Paul of psychics. Conan Doyle claimed to see not only dead family members but fairies as well. He championed photographs taken in 1917 by two girls that purported to show such phantasmal creatures, even though, as one of the girls later admitted, “I could see the hatpins holding up the figures. I’ve always marvelled that anybody ever took it seriously.” Conan Doyle, however, was convinced, and even published a book called “The Coming of Fairies.” He opened the Psychic Bookshop, in London, and told friends that he had received messages that the world was coming to an end. “I suppose I am Sherlock Holmes, if anybody is, and I say that the case for spiritualism is absolutely proved,” he declared. In 1918, a headline in the Sunday Express asked, “IS CONAN DOYLE MAD?”

  For the first time, Green struggled to rationalize his subject’s life. In one essay, he wrote, “It is hard to understand how a man who had stood for sound common sense and healthy attitudes could sit in darkened rooms watching for ectoplasm.” Green reacted at times as if his hero had betrayed him. In one passage, he wrote angrily, “Conan Doyle was deluding himself.”

  “One thing Richard couldn’t stand was Conan Doyle’s being involved with spiritualism,” Edwards said. “He thought it crazy.” His friend Dixon Smith told me, “It was all Conan Doyle. He pursued him with all his mind and body.” Green’s house became filled with more and more objects from Conan Doyle’s life: long-forgotten propaganda leaflets and speeches on spiritualism; an arcane study of the Boer War; previously unknown essays on photography. “I remember once, I discovered a copy of ‘A Duet with an Occasional Chorus,’ ” Gibson said. “It had a great red cover on it. I showed it to Richard and he got really excited. He said, ‘God, this must have been the salesman’s copy.’ ” When Green found one of the few surviving copies of the 1887 Beeton’s Christmas Annual, with “A Study in Scarlet,” which was worth as much as a hundred and thirty thousand dollars, he sent a card to a friend with two words on it: “At last!”

  Green also wanted to hold things that Conan Doyle himself had held: letter openers and pens and spectacles. “He would collect all day and all night, and I mean night,” his brother, Scirard, told me. Green covered many of his walls with Conan Doyle’s family photographs. He even had a piece of wallpaper from one of Conan Doyle’s homes. “ ‘Obsession’ is by no means too strong a word to describe what Richard had,” his friend Nicholas Utechin, the editor of The Sherlock Holmes Journal, said.

  “It’s self-perpetuating and I don’t know how to stop,” Green confessed to an antiques magazine in 1999.

  By 2000, his house resembled the attic at Poulton Hall, only now he seemed to be living in a museum dedicated to Conan Doyle rather than to Holmes. “I have around forty thousand books,” Green told the magazine. “Then, of course, there are the photographs, the pictures, the papers, and all the other ephemera. I know it sounds a lot, but, you see, the more you have, the more you feel you need.”

  And what he longed for most remained out of reach: the archive. After Dame Jean died, in 1997, and no papers materialized at the British Library, he became increasingly frustrated. Where he had once judiciously built his conjectures about Conan Doyle’s life, he now seemed reckless. In 2002, to the shock of Doyleans around the world, Green wrote a paper claiming that he had proof that Conan Doyle had had a tryst with Jean Leckie, his delicately beautiful second wife, before his first wife, Louisa, died of tuberculosis, in 1906. Though it was well known that Conan Doyle had formed a bond with Leckie during his wife’s long illness, he had always insisted, “I fight the devil and I win.” And, to maintain an air of Victorian rectitude, he often brought along chaperones when he and Leckie were together. Green based his allegation on the 1901 census, which reported that on the day the survey was taken Conan Doyle was staying at the Ashdown Forest Hotel, in East Sussex. So, too, was Leckie. “Conan Doyle could not have chosen a worse weekend on which to have a private tryst,” Green wrote. Yet Green failed to note one crucial fact also contained in the census report—Conan Doyle’s mother was staying in the hotel with him, apparently as a chaperone. Later, Green was forced to recant, in a letter to The Sherlock Holmes Journal, saying, “I was guilty of the capital mistake of theorising without data.”

  Still, he continued to lash out at Conan Doyle, as Conan Doyle once had at Sherlock Holmes. Edwards recalled that, in one conversation, Green decried Conan Doyle as “unoriginal” and “a plagiarist.” He confessed to another friend, “I’ve wasted my whole life on a second-rate writer.”

  “I think he was frustrated because the family wasn’t coming to any agreement,” Smith said. “The archive wasn’t made available, and he got angry not at the heirs but at Conan Doyle.”

  In March of 2004, when Green hurried to Christie’s after the auction of the papers was announced, he discovered that the archive was as rich and as abundant as he’d imagined. Among the thousands of items were fragments of the first tale that Conan Doyle wrote, at the age of six; illustrated logs from when Conan Doyle was a surgeon on a Scottish whaling ship, in the eighteen-eighties; letters from Conan Doyle’s father (whose drawings in the asylum resembled the fairies that his son later seized upon as real); a brown envelope with a cross and the name of his dead son inscribed upon it; the manuscript of Conan Doyle’s first novel, which was never published; a missive from Conan Doyle to his brother, which seemed to confirm that Green’s hunch had been right, and that Conan Doyle had in fact begun an affair with Leckie. Jane Flower, who helped to organize the papers for Christie’s, told reporters, “The whereabouts of this material was previously unknown, and it is for this reason that no modern-day biography of the author exists.”

  Meanwhile, back at his home, Green tried to piece together why the archive was about to slip into private hands once more. According to Green’s family, he typed notes in his computer, reexamining the trail of evidence, which he thought proved that the papers belonged to the British Library. He worked late into the night, frequently going without sleep. None of it, however, seemed to add up. At one point, he typed in bold letters, “STICK TO THE FACTS.” After another sleepless night, he told his sister that the world seemed “Kafkaesque.”

  Several hours before Green died, he called his friend Utechin at home. Green had asked him to find a tape of an old BBC radio interview, which, Green recalled, quoted one of Conan Doyle’s heirs saying that the archive should be given to the British Library. Utechin said that he had found the tape, but there was no such statement on the recording. Green became apoplectic, and accused his friend of conspiring against him, as if he were another Moriarty. Finally, Utechin said, “Richard, you’ve lost it!”

  One afternoon while I was at my hotel in London, the phone rang. “I need to see you again,” John Gibson said. “I’ll take the next train in.” Before he hung up, he added, “I have a theory.”

  I met him in my hotel room. He was carrying several scraps of paper, on which he had taken notes. He sat down by the window, his slender figure silhouetted in the fading light, and announced, “I think it was suicide.”

  He had sifted through the data, including details that I had shared with him from my own investigation. There was mounting evidence, he said, that his rationalist friend was betraying signs of irrationality in the last week of his life. There was the fact that there was no evidence of forced entry at Green’s home. And there was the fact, perhaps most critically, of the wooden spoon by Green’s hand.

  “He had to have used it to tighten the cord” like a tourniquet, Gibson said. “If someone else had garroted him, why would he need the spoon? The killer could simply use his hands.” He continued, “I think things in his life had not turned out the way he wanted. This Christie’s sale simply brought everything to a head.”

  He glanced nervously at his notes, which he strained to see without his magnifying glass. “That’s not all,” he said. “I think he wanted it to look like murder.”

  He waited to assess my reaction, then went on, “That’s why he didn’t leave a note. That’s why he took his voice off the answering machine. That’s why he sent that message to his sister with the three phone numbers on it. That’s why he spoke of the American who was after him. He must have been planning it for days, laying the foundation, giving us false clues.”

  I knew that, in detective fiction, the reverse scenario generally turns out to be true—a suicide is found to have been murder. As Holmes declares in “The Resident Patient,” “This is no suicide.… It is a very deeply planned and cold-blooded murder.” There is, however, one notable exception. It is, eerily enough, in one of the last Holmes mysteries, “The Problem of Thor Bridge,” a story that Green once cited in an essay. A wife is found lying dead on a bridge, shot in the head at point-blank range. All the evidence points to one suspect: the governess, with whom the husband had been flirting. Yet Holmes shows that the wife had not been killed by anyone; rather, enraged by jealousy over her husband’s illicit overtures to the governess, she had killed herself and framed the woman whom she blamed for her misery. Of all Conan Doyle’s stories, it digs deepest into the human psyche and its criminal motivations. As the governess tells Holmes, “When I reached the bridge she was waiting for me. Never did I realize till that moment how this poor creature hated me. She was like a mad woman—indeed, I think she was a mad woman, subtly mad with the deep power of deception which insane people may have.”

  I wondered if Green could have been so enraged with the loss of the archive that he might have done something similar, and even tried to frame the American, whom he blamed for ruining his relationship with Dame Jean and for the sale of the archive. I wondered if he could have tried, in one last desperate attempt, to create order out of the chaos around him. I wondered if this theory, however improbable, was in fact the least “impossible.”