How Holmes Solved "The Adventure of the Parisian Pasteboards"

Dearest Detectives,

We thank you all for joining us on our latest endeavor. The Adventure of the Parisian Pasteboards certainly took us on an unexpected journey, but thankfully, our missing men simply turned out to be men on a mission. It does, however, seem like the Sûreté’s evidence room will be short a clerk until things in Japan settle down. As per usual, we've returned to find countless excellent theories awaiting in our mailbox. While we comb through our newest Featured Detective entries, why not compare your theory to Holmes’ own solution – did everything line up as hypothesized? 

Looking forward to our next case, 

The Dear Holmes Team

——

13 May, 1888

Lt. D’Orsay,

I daresay I have had success in interpreting your Parisian pasteboards and can confirm: your friend ‘G’ was offering sincere advice. When you first wrote to me about Aurand, I had, as you suggested, already known of the ‘disappearance ’. At the time, however, I imagined he was but a disinterested officer who had grown weary of his post. I reconsidered this notion after receiving your first communique and learning of the pasteboard he left behind. I began investigating Henri Aurand’s past in Japan, and with the Armée, but as you had mentioned, he seemed to be a rather unremarkable soldier.

Your second letter then provided much needed clarity. The newly missing Neuchatel, like Aurand, clearly shared ties to Japan and these pasteboard placards. I suspected that your two men, and their disappearances, might be rather closely entwined; your visit to Le Loup Mordant bolstered my confidence in this theory. It not only provided insight on what we now know was a ‘méreau’, but also unwittingly identified a key individual: Valmont. I again turned my focus to the pasteboards; perhaps these men were using them to communicate their destinations. But I could make no sense of the hole-punched patterns. Thankfully, your third letter provided a trove of information that enabled me to not only verify that Neuchatel and Aurand both lived double lives, but also fully decipher the cards left behind in their places.

Mycroft’s research had found that our missing men both worked in Tokyo at the same time. Meanwhile, the letter that had been sent to Neuchatel’s dormitory revealed his secret engagement to Mlle. Camille Lavier, a resident of Ichigaya’s French quarter. Japan appeared to be a sure destination for at least one of the two men. Their reason for travel became apparent once I deciphered their placards’ messages, which your second visit to Neuchatel’s dormitory made possible. The small collection of books you had noted in the young scholar’s chamber pointed me in the direction of the Napoleon cipher, also known as a ‘pigpen’ cipher, and otherwise the key to these vexatious placards (more on this to follow). Knowing this, the case quickly began to unravel.

The first message, left behind by Aurand, tied Neuchatel and ‘Minotaur’ to Aurand and Ichigaya. Otherwise, it offered little insight alone. It reads: KENPEITAI IN ICHIGAYA, MINOTAUR, NEUCHATEL. The second pasteboard, found in Neuchatel’s waste bin, was more concerning, though still rather uninformative if read independently: VALMONT IN NEW GAPSIN, KENPEITAI KNOW. The third, which lacked a number, proved to be most intriguing. Besides its missing component, it had been left behind for someone who never came, rather than in place of someone now gone. This suggested that the numbers– which functioned as an additional layer of encryption– were not being written by the author of these messages. Rather, they were being added by the readers upon obtaining the placards.

Your interview with the Hotel Britannia maid, Mlle. Delmas, was able to shed further light on this, as well as on the person who delivered the third placard. I posit that the young man whom Mlle. Delmas oddly recognised was M. Neuchatel, who often makes public appearances with his father. She recalled that the young man had visited roughly a week prior to your interview with her, which was just about when Neuchatel ‘vanished’. At the time, he insisted that the card be left untouched in Room #207. This was simply because the room number is meant to designate each card’s ‘missing’ numeral. In fact, Mlle. Delmas’ experience with the placards leads me to believe that the hotel’s second story alone was being used as a consistent drop site. That would allow for the use of twelve distinct numbers for this purpose. The letter that Neuchatel left behind was meant to be deciphered with the number 7, and warned: VALMONT LYING, MINOTAUR UNSAFE, THESEUS PROTOCOL. With this message, I was finally able to start drawing definitive lines between Valmont, our missing men, and ‘Minotaur’.

The true nature of their relationships was ambiguous, but I strongly suspected that ‘Minotaur’ referred to a group of agents. A group which identified itself with a small méreau depicting a ‘bullheaded figure’, otherwise known as a minotaur. And as per the third pasteboard message– referencing Theseus, slayer of the minotaur– a group which would soon cease to exist. The intelligence gathered in your final letter illuminated these details, while also allowing me to view the placards under a wholly different light.

My brother’s information verified that Jules Valmont had at least three active subordinates besides Aurand. These men– including Aurand– were the ‘Minotaur’. They had once been assembled by Valmont, who was presently overseeing an operation from a small headquarters in Ichigaya’s Panhard-Levassor factory. The foreign payments received by the Hotel Britannia originated from these headquarters, and were being carried out with Japanese notes so as to curtail any possible connections back to France. Boniface’s placards then gave much needed context to the situation. The message found by his colleagues, which had prompted his departure, reads as follows: VALMONT ROGUE, HELP KPT, APPREHEND. The older one, which you discovered in his bureau, relayed the message: COUVIER GONE, MEREAU AT HOTEL, BE ON GUARD. Evidently, Boniface had been aware of their other missing compatriot, Couvier, as had Aurand. These placards also made it clear that Valmont was not to be trusted, and confirmed that our missing men were, at least in part, assisting Japan’s Kenpeitai with a shameful turn of events. That is, the discovery of Valmont’s unofficial independent project (the ‘New Gapsin’ described by the second pasteboard) and his subsequent absconsion.

Referring to the placards by the order in which you discovered them (Placards 1 through 5), we may now track Aurand’s journey from the start. I conjecture that both of Boniface’s pasteboard messages (Placards 4 and 5) were sent by Aurand, who knew of the méreau found at the Hotel Britannia. Realising that Couvier was unaccounted for, Aurand first used Placard 5 to inform Boniface and caution him to ‘be on guard’. Then, Aurand found Placard 1, which drew his attention to the Kenpeitai in Ichigaya. Valmont was attempting to employ the members of Minotaur in his unofficial project, and enlist Aurand’s own subordinate, Neuchatel. It would not surprise me if Couvier, Duvalle, or even Boniface, received similar placards at that time.

Had there been any delays in the Kenpeitai’s investigation, Valmont may have succeeded in deceptively assembling his subordinates. However, by the time Aurand actually arrived at Ichigaya, the Kenpeitai were already investigating Minotaur’s Japanese headquarters. They had uncovered Valmont’s plot, causing the man to flee, and casting doubt upon Aurand and the rest of his associates. Understanding that peace between Japan and France is yet delicate, Aurand began helping the Kenpeitai locate Valmont without question. But first, he sent notice of Valmont’s conspiracy to Neuchatel (Placard 2) and Boniface (Placard 4), even summoning the latter to help apprehend him. M. Neuchatel subsequently warned any other members of the group by placing Placard 3 at the Hotel Britannia.

The messages themselves were, as stated, masked with a variation of the classic ‘pigpen’ cipher, wherein the letters of the alphabet can be placed within several grids, so that each facet of the grids can be identified with a pictogram. The so-called grids are much like the ones you found etched in Boniface’s cabinet— I have drawn a complete example on the reverse side of this page. The ‘pictograms’, in this case, can be easily discerned if one considers the hole punch ‘patterns’ as discrete three-by-three sets. Finally, the numbers handwritten on the placards signify an amount by which one should displace each pictogram’s corresponding letter. So a pictogram referring to the letter ‘A’, on a placard marked ‘8’, might actually refer to either ‘I’ or ‘S’. Once the recipient figures out whether to shift their results forwards or backwards, the cipher becomes rather simple.

Lt. D’Orsay, in the coming weeks, I expect your clerk, Aurand, will return with a masterfully convenient excuse. As for M. Neuchatel, I advise that your colleagues ensure his beloved is apprised of his well being. Mlle. Lavier would appreciate knowing that the young man has not simply grown wary of their engagement. I expect the Sûreté will be able to proceed as always until this misadventure has been brought to a close. However should you find yourself in need of an additional pair of hands in the evidence room, do not hesitate to send word– Watson still dreams of the Meursault we tried there last year. I am certain he would be amenable to most any offer promising a return to Paris.

Sincerely,

P.S. If need be, reference the chart below when deciphering the messages.