Invasion

He had no cipher materials: possession of such in any context was prima facie evidence of espionage. Yet if the communications were not enciphered he could not risk divulging vital and necessary details. In any case, to meet Fulton's demands he had to obtain a written undertaking at the highest level, which must be secure. He was going round in circles. There must be a way.

Renzi was by no means ignorant of secret codes after his experiences in Jersey: could he find a method from first principles to encrypt the message? The gravest difficulty of all was that in virtually every case the key had to be known beforehand at the receiving end or it must be sent in clear by other means—with catastrophic consequences if compromised.

Despite everything, Renzi found himself drawn into the logical challenges of the dilemma. After the intense boredom of the prisoner-of-war negotiations, the danger and frustration of dealing with Fulton, this bracing intellectual exercise was congenial, and he bent his mind to the task.

Any cipher whose key could be discovered was by definition unusable. Classical ciphers, such as the famous Caesar Shift, with no key but letter substitution, were unsafe—code-breaking had moved on in modern times. The same applied to the transposition types and, without prior arrangements, more complex techniques would require a key or method-type to be sent on before in clear.

A book cipher? This had the advantage that the key was already in the possession of the receiver—the text of a pre-agreed book held by both. A word in the message was specified as a precise location of that same word in the book. The disadvantage was that not only was it essential for each to have precisely the same edition but it was laborious, and the resulting encipherment could be large in size. The Bible had been used many times, with its exact chapter and verse convenience, but of course it would be the first that code-breakers tried.

There was another method: the running-key cipher. This used a source book too, but at individual character level. From a given point the ongoing text was used as a continuous key-stream to yield coded values against the message contents. This was better—and if the book's title was protected the resulting encipherment was near unbreakable.

So, what volume was to be used, known precisely by both parties? The Admiralty's own King's Regulations? Or the Articles of War? But without them to hand he could not swear to accuracy. And if it was to be some other book, its name and edition had to be divulged first. He was back where he had started.

He lay down and closed his eyes. It was the separate transmission in clear of a key or decoding method that was the sticking point. If he could only—

He sat bolt upright. That was it! The method, the key-text—and a cast-iron secure way of transmitting the key!

Galvanised, he set to work. He would not be disturbed—he had uncovered some time ago that Haslip's concern to be left alone was on account of a certain woman, and the French could not trespass on diplomatic territory.

Snatching up paper and a pencil he began to set up his tabula recta, the encoding matrix. Not needing to consult a book, he was able to work swiftly, and at a little after midnight he had the result. Carefully he burned his workings, folded the papers as small as he could and sealed them tightly together.

He hesitated over the forwarding instructions but eventually settled on 'Foreign Office, per Smith, Paris.' It would find the right handler easily enough. Underneath, in smaller lettering, was the more important entry: 'Refer Cdr Thomas Kydd, HMS Teazer.' It was done.

Kydd stalked into his cabin in a foul mood. This was the third man flogged within the month for petty crimes, unavoidably in full view of the shore, and the spirit aboard was stagnating. When would the damned timbers arrive for the repair? He was keenly conscious of the fearful danger under which England lay and it went so much against his grain to lie in useless idleness. And Renzi—heaven knew what he was up to, and would Kydd ever find out?

Restless, he ventured on deck again. A fine sight, so many blue-water ships, particularly the big Indiaman to the south—as massive as a line-of-battle ship with, no doubt, a freighting aboard worth a prince's ransom, and soon to venture out to the open ocean where dangers lurked in wait every day of her six months', or more, voyaging.

Ashore, he could pick out the Deal hovellers. On this fine summer's day there was nothing to occupy them except the taking out of fresh provisions, passengers—

'Telegraph's in a taking,' Hallum offered, behind him, trying to make conversation. The shutter atop a bluff tower in the King's Naval Yard was indeed busy, clacking away furiously. The chain of signal stations stretched all the way to London and the Admiralty in a direct line.

Idly, Kydd wondered what it was signalling. Never used for routine messages it was how the first lord of the Admiralty, through his senior staff, was able to reach out and deploy the chess pieces that were his fleets to counter enemy threats. Incredibly, this signal would be here, in the commander-in-chief's hands, some fifteen minutes or so after it was sent from London.

He resumed pacing. It was no use worrying about his timber, which would come in its own good time. He must contain his impatience and be ready to throw Teazer into the fray the instant she was whole once more.

'Boat approaching, sir.'

Oddly, the vessel had been launched from the King's Naval Yard instead of the flagship, and with only a single officer in the sternsheets. Kydd stayed on deck and watched it hook on.

The officer came on board. 'Commander Kydd, sir?' he asked respectfully, with more than a hint of curiosity.

'It is.'

'Then, sir, I have a message from the admiral. You are to hold yourself in readiness at his office immediately for a particular service that he will speak to you about—in person.'

'Er—'

'I know nothing further.'

'Very well.'

Admiral Keith was short, almost to the point of rudeness. 'Kydd, I have just received a signal from the Admiralty concerning you that greatly disturbs me.'

'Sir?' The Admiralty?

'It asks—no, damn it, demands that you be taken out of your ship and made ready to