"The what?"
"The Master Incarnate, which is what the leader of this devilish organization calls himself. You may wonder why I believe this of d'Hiver on so little apparent evidence. The inductive chain is a strong one, and the links are sound. The members — if I may call them that — of the Hellfire Club must wear masks when physically present at the club, and thus do not know one another's identities. It is one of the strictest of this despicable organization's rules. The only person who knows the name of a member, except for the one who proposed him, is their chief, the Master Incarnate."
"And so?" Barnett asked, feeling that he had lost one of the links of Moriarty's chain.
"And so, Mr. Barnett, the only person who could have known, by their names, that the victims of our mad magician were all members of the Hellfire Club is the Master Incarnate. Since none of the victims seems to have taken unusual precautions for his safety before he was killed, I think we can assume that the Master Incarnate did not pass on to his disciples the fact of their mortal danger. But he himself must have been at least intensely curious as to who was killing off his membership.
"If we assume the Master Incarnate to be d'Hiver, it would explain his passionate interest in the progress of Holmes's murder investigation, and his clandestine presence outside this house in response to my advertisement. From which he must have assumed greater knowledge on our part than we actually possessed. It would, therefore, explain his attack on poor Holmes. He must have panicked when he saw Holmes leave this house. Had he time for reflection, I am sure he would not have done so. Although he does seem to have come prepared to attack someone."
"Wasn't he afraid of being recognized, sitting out there?" Barnett asked.
"I would assume he was in disguise," Moriarty said. "Remember, the Mummer identified him by an overheard name, not by his appearance."
Barnett rose and refilled his own coffee cup. Then he resumed his seat and sipped quietly while he thought over Moriarty's notions. "What about this code?" he asked.
"Ah, yes," Moriarty said, removing a bulky object from his outside jacket pocket and passing it across the table to Barnett. "I wondered when you would ask. Please examine this; on it I base my case."
Barnett took the bulky object and found that it was the "Jarvis & Braff Compleat Map of the Great Metropolis of London & Its Environs, Showing All Omnibus, Tramway, and Underground Lines As Well As Points of Interest" closed with its special "Patented Fold."
"What is this?" Barnett asked, after staring at it for a minute and extracting no meaning beyond that declaimed on the cover.
Moriarty sighed. "It is a map," he said. "It is also what we codebreakers call a 'key.' "
Barnett unfolded the map, which was closed with a sort of zigzag accordion pleat. It appeared to be no more than what it advertised: a map of London. "Is this the 'key' you were talking about last night?"
The professor nodded. "It is."
"That's wonderful," Barnett said, spreading the map out on the table. "Just what does it say?"
"It gives us the current location of the Hellfire Club," Moriarty explained. "They don't stay in any one place very long. They wouldn't want to take any chances on the neighbors' getting too friendly. But then they have the problem of informing their membership of the new location of the, for want of a better term, clubhouse."
"This map," Barnett said, gesturing at the large five-color rectangle on the table before him, "gives the location of every place in London. But it isn't specific, that I can see."
"No," Moriarty agreed. "But the code message in the agony column pins it down."
"How does it work?"
"It is ingeniously simple." Moriarty rose and left the dining room for a second, returning with an eighteen-inch steel rule from his study. "I'll let you work it out for yourself." He tossed the rule to Barnett. "Let us start with the message found on the late Lord Walbine. 'Fourteen point four by six point thirteen.' What do you make of that?"
Barnett took out his pencil and jotted the numbers down on the margin of the map. "Measurements," he said. "That's it," Moriarty agreed.
"Well, it wasn't very hard to figure that out after you handed me a ruler," Barnett said. "But just what do I measure?"
"There are several possibilities." Moriarty said. "Top, bottom, either side; or, for that matter, from some arbitrary point on the map — say the tip of the Tower, or the gate of the Middle Temple. Luckily for us, they were not that subtle. Measuring in from the left side and then down from the top will accomplish our purpose."
Barnett held the ruler uncertainly, staring down at the map. "I'm not sure—" he said.
"It's the lack of scientific training," Moriarty said. "Scientists are never at a loss as to how to mark up someone else's papers. I suggest you start by marking the first measurement along both the top and bottom margins of the map. Notice that the ruler is marked off in inches and sixteenths. I assumed those were the proper fractions, as it is the common marking for such rules, and I was proved to be right. So your first measurement is fourteen and four-sixteenth inches from the left-hand border."
Barnett marked this distance carefully along the top edge, and then again along the bottom, as Moriarty instructed. Then he laid the rule carefully between the two marks, and measured six and thirteen-sixteenths inches down from the top, marking the place with a small pencil dot. "I see you've been here ahead of me," he said, noting a second small dot almost directly under his.
"Babbington Gardens," Moriarty said. "Northwest corner."
"That's what I get," Barnett affirmed.
"Well, that was my first stop this morning," Moriarty said. "My assumption was that the final number — three-four-seven — was the identification of the proper building, and, therefore, almost certainly the house number. Two houses in from the corner, along the east side of the street, I found it. It is, at present, untenanted. Certainly strongly suggestive, if not proof positive."
"Didn't you break into the house to look around?" Barnett asked.
"Certainly not!" Moriarty said, looking faintly amused. "That would be illegal. But I did speak to the tenants in the houses to either side."
"You did?"
"In the guise of a water-meter inspector. It never ceases to amaze me what information people will gladly give to a water-meter inspector. I learned that the house was occupied until mid-March, that it would seem to have been used as some sort of club, that gentlemen came in carriages at all hours of the evening and through the night, and that on occasion strange noises were heard to emanate from somewhere inside. I also learned that neighbors who attempted neighborly visits were rudely rebuffed at the door."
"That sounds as if it must be the right place," Barnett said.
Moriarty nodded agreement. "It would be stretching the bounds of credulity to assume it to be a coincidence," he said. "But just to be sure, I then went to the location derived from the Hope Newspaper."
Barnett roughly measured off the distances indicated, and found Moriarty's pencil mark on the map. "Gage Street," he said. "How accurate is this system, Professor?"
"If you are careful in your measurements, it is sufficiently accurate for the needed purpose."
"Well, if that is so," Barnett asked, "then how secure is the code? If you found it this fast, why haven't others?"
"They have to know what to look for," Moriarty said. "Even if someone should guess that it is a map coordinate code he would have to know what map to use."
"You did," Barnett said.
"I had a list of the effects of the murdered men," Moriarty said. "Two of them had Jarvis & Braff maps close enough to their persons when killed to have them mentioned on the inventories."