‘Hello,’ said Holmes, standing behind me. ‘It seems they mean business. I suppose Jackie Fisher or Reggie Esher alone might suggest a pleasant social visit. Two of them together can only mean trouble of some kind.’
Presently there was a knock at the door and Mrs. Hudson, more flustered than was customary, ushered in our two distinguished visitors. There was a cordial babble of greetings, in the course of which I was introduced to Lord Esher, whom I had already recognised from his photograph in the
Illustrated London News
of the previous week. Then, from the depths of the armchair in which my friend had installed him, Fisher said: ‘My dear Holmes, I must come to the point of our visit with somewhat indecent haste. In a moment you will understand why. So far, the full details of this matter are known only to Esher and myself—and to one other person whose identity you will readily guess.’
‘Not Mr. Asquith, I think,’ Holmes interrupted sardonically.
Esher shook his head.
‘No, gentlemen. Not even the prime minister is privy to the entire story. We are here with the knowledge and approval of King Edward himself. It seems that he reposes a good deal of confidence in the name of Sherlock Holmes.’
I thought that Holmes sounded a little too suave in his reply.
‘I was able to render His Majesty a small service some years ago in the so-called Baccarat Scandal. A most disagreeable affair of an officer and gentleman cheating at cards in his presence. It came, in the end, to a trial for libel. The Prince of Wales, as His Majesty then was, had been required to give evidence.’
Fisher turned a little and stared at him directly.
‘Cast your mind back to certain other cases that came your way at the time. The affair of the Naval Treaty, the blackmail of a crowned head by Miss Irene Adler, and, perhaps especially, the disappearance of the secret plans for the Bruce Partington submarine.’
‘Naturally I still have the papers relating to every case.’
Fisher’s impatience was a driving force of his character. He turned to Holmes.
‘Never mind the papers. Did you—then or at any other time—acquire information relating to the ciphers of the German High Seas Fleet?’
‘Or any German system of codes, come to that,’ added Lord Esher quietly.
Holmes looked at them for a moment as if he suspected a trick. He had filled his pipe but, perhaps out of deference to our guests, had not yet lit it.
‘The Imperial German Navy has had nothing to do with any case of mine,’ he said presently, waving a match to extinguish it.
‘So far as I am aware.’
There was no mistaking the disappointment in the faces of our two visitors.
‘However,’ he continued, ‘a practical working knowledge of coded messages is certainly necessary in my profession. I have deciphered the hieroglyphics of the Dancing Men and the riddle of the Musgrave Ritual. As you are no doubt aware, my solution in the Musgrave case led to the recovery of the ancient crown of the kings of England, lost by the Royal Stuarts after the execution of Charles I. You may also care to take away with you a small monograph of mine on the use of secret communications in the war of Greece against Persia during the fifth century
BC
. Despatches from Athens to Sparta were sent as meaningless strings of letters on a strip of cloth. When the strip was wound round a particular wooden baton, in a spiral and at precisely the angle known only to the sender and the recipient, the random letters formed themselves into words.’
‘Very interesting, Mr. Holmes,’ said Lord Esher, who looked as though he did not find this story interesting in the least. ‘The question is whether, from your experience or your researches, you can break the German naval code—and do it within the next fortnight.’
‘If it is to be done, by all means let it be done quickly,’ Holmes replied with that languid air of self-assurance that so irritated both his adversaries and Scotland Yard. ‘I daresay any fool could do it, given time. A fortnight sounds like a generous allowance for a man of moderate intelligence.’
‘I have to tell you,’ Fisher interposed, ‘that our best cryptographers at the Admiralty have tried for two months without success.’
‘That does not surprise me in the least. Pray tell me what, if anything, is known about these most interesting ciphers. What are they used for?’
The First Sea Lord and Viscount Esher looked at one another and, by the slightest change of expression, seemed to agree silently that they must reveal more than they had intended.
‘Our instructions …’ Fisher began.
‘From His Majesty, I presume?’
‘Our instructions are to tell you all that you may need to know in order to accomplish this. You will also understand why it must be done. It seems that we have a spy at the very heart of Admiralty intelligence. He has apparent access to warship design, speed, gunnery performance, and the devil knows what else. Let us not be self-righteous about it. I may tell you in strictest confidence that we have our own man in Berlin. He makes his reports to our naval attaché at the embassy.’
‘I should have been surprised had it not been so,’ said Holmes equably.
‘According to this source, information is being passed by the traitor in our ranks to an enemy agent in this country. The encrypted messages are then transmitted by Morse code over a relatively short distance. We must assume that they are picked up by a German naval vessel in international waters, perhaps no more than five or ten miles from Dover or Harwich. The coded transcript then goes to the Ministry of Marine in Berlin, to the Wilhelmstrasse. Our man there has no official access to decoded messages and has seen only two, at considerable risk. Both related to Royal Navy gunnery signals. He has seen a number of transcripts, still encoded, and provided us with sequences of letters. These match certain sequences in Morse transmissions that our monitors have intercepted. It has been impossible to decipher more than a few words in all. Even that is mere luck. It seems plain that the code not only differs in every transmission; it differs from word to word in a single message.’
‘His Majesty is determined,’ added Esher, ‘that the turncoat in our service shall be hunted out and put behind bars in the shortest possible time. He regrets only that in time of peace the scoundrel cannot be hanged or shot.’
Holmes raised his eyebrows.
‘Have a care, my lord! With my humble duty to His Majesty, he must do no such thing as hunt the rascal out and expose him to the world. Do you not see? In this game, the turncoat is your most valuable piece upon the board. If you can pick him out and leave him be, all may yet be well. If he is clapped behind bars, Tirpitz will close down the entire business and you will have lost the only thread that guides you through the maze. Let well alone.’
I do not think Lord Esher, to judge from the expression on his face, relished returning to his royal master and telling him that Sherlock Holmes thought his instructions mistaken.
‘If time is at a premium,’ said Holmes enthusiastically, ‘may we have sight of these unusual documents?’
Sir John Fisher cast his eyes round the room. The disagreeable truth was that there was no surface large enough to display the transcripts except the worktable of Sherlock Holmes. This disreputable piece of furniture was stained by overzealous chemical experiments, while a medical scalpel lay in a butter dish, near a dismantled Eley revolver and a blood-stained nightstick peeping from its newspaper wrapping. Unabashed by this, Holmes all but swept the contents of the table to the floor in his eagerness to have the coded messages before him.
We arranged four chairs round the table. Admiral Fisher opened his briefcase. A folder containing fifty or sixty transcriptions of intercepted transmissions was laid before us. If I describe the first, it will do for all the rest. There were no words, merely blocks of fourteen letters at a time. The first line may suffice.
WTRYILJGDVJNLS DDPYUGSHMKRWEX CNBJJUSDTINCRL
How on earth such drivel could contain details of warship design, gunnery trials, speed at full steam, diesel consumption, and armored plating was beyond me. Fisher looked up at us.
‘You may save yourselves the trouble of trying to substitute one letter of the alphabet for another. Our cipher clerks have run the entire gamut in the past few months.’
‘I should not dream of such a thing.’ Holmes stood and walked across to the window in easy strides. He turned and came back towards us. ‘The message may elude us at the moment. The nature of the code can scarcely be in doubt.’
‘Can it not?’ asked Esher skeptically. He was in no mood to let Holmes play the prima donna at such a time as this.
Holmes sat down again. ‘If your information is correct, it is quite plainly a looking-glass code.’
‘Perhaps you had better explain that,’ said the First Sea Lord uneasily.
Holmes looked from Sir John to Esher.
‘As sender and recipient, you would each have a copy of the same piece of plain text. It would probably be a page from a book, a novel, or the Holy Bible perhaps. That would be the key to the cipher. Let us suppose that you wish to send Lord Nelson’s famous signal at Trafalgar, “England expects.” Let us also imagine that the first words of the cipher key in the hands of each of you are “In the beginning.” Now, line up the two phrases. Your signaller will not want to transmit for longer than necessary. Therefore, for speed and convenience, you may construct a grid of the alphabet beforehand, running
A
to
Z
across the page and
A
to
Z
down the left-hand margin.’ Sherlock Holmes’s long bony fingers worked deftly with pencil and ruler on a plain sheet of paper.
CIPHER KEY:IN THE BEGINNING
SIGNAL: ENGLAND EXPECTS
A B C D E F G H I J K L M N O P Q R S T U V W X Y Z
B C D E F G H I J K L M N O P Q R S T U V W X Y Z A
C D E F G H I J K L M N O P Q R S T U V W X Y Z A B
D E F G H I J K L M N O P Q R S T U V W X Y Z A B C
E F G H I J K L M N O P Q R S T U V W X Y Z A B C D
F G H I J K L M N O P Q R S T U V W X Y Z A B C D E
G H I J K L M N O P Q R S T U V W X Y Z A B C D E F
H I J K L M N O P Q R S T U V W X Y Z A B C D E F G
I J K L M N O P Q R S T U V W X Y Z A B C D E F G H
J K L M N O P Q R S T U V W X Y Z A B C D E F G H I
K L M N O P Q R S T U V W X Y Z A B C D E F G H I J
L M N O P Q R S T U V W X Y Z A B C D E F G H I J K
M N O P Q R S T U V W X Y Z A B C D E F G H I J K L
N O P Q R S T U V W X Y Z A B C D E F G H I J K L M
O P Q R S T U V W X Y Z A B C D E F G H I J K L M N
P Q R S T U V W X Y Z A B C D E F G H I J K L M N O
Q R S T U V W X Y Z A B C D E F G H I J K L M N O P
R S T U V W X Y Z A B C D E F G H I J K L M N O P Q
S T U V W X Y Z A B C D E F G H I J K L M N O P Q R
T U V W X Y Z A B C D E F G H I J K L M N O P Q R S
U V W X Y Z A B C D E F G H I J K L M N O P Q R S T
V W X Y Z A B C D E F G H I J K L M N O P Q R S T U
W X Y Z A B C D E F G H I J K L M N O P Q R S T U V
X Y Z A B C D E F G H I J K L M N O P Q R S T U V W
Y Z A B C D E F G H I J K L M N O P Q R S T U V W X
Z A B C D E F G H I J K L M N O P Q R S T U V W X Y
He worked with such intensity that I swear, for the moment, he had forgotten any of us was there. Then he looked up.
‘I do not find such a grid essential, but few people are trained to encode messages in their heads. Very well, then, gentlemen. “England expects” and “In the beginning.” Take the first letter of each. If you will follow my pencil tip, you will see that a downward line from
E
on the top horizontal line and an inward line from
I
in the left-hand vertical column will meet at
M
. The first letter of our encoded signal is therefore
M
. Following the same process with the second letter of the signal and the cipher,
N
and
N
meet at
A
. Perhaps you will take it from me that if you follow the remaining letters and note where their lines meet on the grid,
ENGLAND EXPECTS
is encoded as
MAZSEOH KFCRKGY
.’
It seemed to me, as the saying goes, that our two guests were trying to hang on to his coattails. Holmes remained composed and self-assured.
‘You will understand the simple advantages of this system at once. The message is transmitted as
MAZSEOH KFCRKGY
. The normal tools of decoding are useless. It will not do for your Admiralty cryptographers or their unseen adversaries to puzzle which letters stand for
A
,
B
,
C
, and so forth. Nor will it help you to look for the frequency with which letters appear, assuming that the most common letter in almost any language is
E
, the next most common
T
, followed by
A
. In my example, our original message contained the letter
E
three times. When encrypted as a looking-glass cipher, however, the first
E
appears as
M
, the second as
K
, and the third as
R
. As for frequency, the only encoded letter which appears more than once is
K
, which stands for
E
on the first occasion and
C
on the second.
T
never appears and
A
only once.’
There was a profound silence, broken at last by Lord Esher.
‘Put as you put it, Mr. Holmes, the whole thing sounds quite ghastly.’