After his breakfast, David placed a trunk call to Hans, telling him he should arrive by eleven thirty if the roads were good and he had no punctures. Next, he telephoned the concierge and confirmed that his car had been refuelled, then asked that it be brought to the door and that his account be ready when he descended in ten minutes.

Then after refreshing in the bathroom, he took three twenty-franc and two ten-franc gold pieces plus an assortment of silver coins from his money belt, before putting on his waistcoat and finishing dressing. With his suitbag rearranged and buckled, he descended to the lobby.

After identifying himself at the reception desk, he was presented with the account. Sixty-five. Less than I expected. He took three of the larger gold pieces and a five-franc silver one from his pocket.

As he walked across the lobby toward the door, he thought: A month's wages for a labourer here, but less than my commission from the ladies' watches. Wilhelm's philandering bought me a restful night, and his loose talk will give London more pieces for their puzzle.

The car was ready, and after kicking the tyres, thumping the three good spares and confirming the fuel gauge, he headed out. Beyond the city gates, he followed the Birs River valley to the Angenstein gorge and through it along the Vallée de Laufen to Delémont and Münster.

During the ascent to Col de la Pierre Pertuis, he shifted down to third, then to second. After clearing the pass, he kept the car in third gear, allowing the engine to slow his descent into Vallon de Saint-Imier. Then through the Gorges du Taubenloch and onto the sun-drenched, south-facing slopes, the air was filled with the scent of pine needles as he coasted downhill toward the broad lake and Bienne.

As he paused for cattle being led across the road, he checked his watch: Ten past eleven. Faster than I thought.

A few minutes later, he stopped the car in front of the stone façade of the Rolex works. Inside, the woman led him along the hall, and as they entered, Hans rose from his desk, extended his hand and said, "Faster than promised, David. Success?"

"On many fronts."

"And ...?"

"He wants nine in gold. Three of each."

Hans chuckled. "Compensating for his tactical failures at Verdun with his generosity in the bedroom."

"So it appears." David smiled. "But the wine loosened his tongue again. He is a lonely man, a marionette moving to the strings above. After the tasting, we shared a private dinner, finishing the remainder of the three bottles."

"Three?"

"I took a white and a red from Sonnenhang – Burgundy Grand Cru quality, hoping they might provide an entrée for another visit. They worked far beyond that."

Hans nodded. "When do you need the watches?"

"He seemed preoccupied, but he mentioned a few weeks – after the situation beyond Verdun had settled."

"Confirming the movement my people had seen."

"Yes, and expect a letter from him – a new pass for me and instructions."

"I will have the watches crafted and assembled immediately, in case ... Will you join me for lunch?"

"Would that I could, but I must be quickly to Bern to send my harvest to London."

After farewells, David headed south out of Bienne, through Lyss and Seedorf, slowing or stopping occasionally for farm wagons and livestock to clear. Then into Bern, across Kirchenfeldbrücke to Elfenau and the Embassy.

Inside, after being let through the side passage, he strode directly to the Ambassador's open door and knocked.

Evelyn looked up from his desk. "Ah, David, come in. Stanley told me you had safely returned."

David took two steps in, then stopped and said, "I must make order of the chaos in my head and send it to London."

"Significant?"

"Extremely so, sir. Far more than I had hoped."

"Come see me after."

David nodded, turned and headed to Bryce's office and said, "Come. I have a frightful mess of bumf in my head that we need to sort, double-encrypt and send."

Bryce stood. "Success, then?"

"You will realise how much so as I pour it out." With Bryce in tow, David continued toward his office. Then inside, with the door locked, he sat in his chair and closed his eyes. "Write down what I pour out, Bryce. I'll try to summarise first, give the jumble some shape, then you can probe me for details."

For more than two hours, they organised and refined David's thoughts into a succinct report, encrypted it with Playfair and used the message's date to double-encrypt with columnar transposition. Then after decrypting random portions to prove accuracy, they took it to the Telegraph Room and handed it to Sergeant Wilkins. "Highest priority. Inform me as soon as it has been receipted. If I'm not in my office, I'll be in the Ambassador's."

"Yes, sir."

David led Bryce back to his office, took a sheath of paper from his pocket, walked to the window, opened it and lifted a large brass bowl onto the windowsill. "Next, we burn these."

"Is there not a vented burner in the Telegraph Office?"

"Yes, but none in there have a need to know."

"Ah, of course." He nodded at the pages. "A mole could sort out the cyphers from that."

"Exactly." The sharp tang of sulfur filled the room as David struck a Welsh match against the underside of the desk. He held the flame to the corner of a lightly crumpled page, watching the fire eagerly take hold. When the edges flared bright orange, he dropped it into the bowl, the breeze off the Aare drawing the whisps of grey smoke out and across the courtyard.

He repeated with each page, and when the last of the flames died, he stirred the curled remains with a letter opener, breaking them into unrecognisable flakes of ash. When satisfied, he tilted the bowl and blew across it, helping the breeze scatter the ash out over the gardens below.

Then glancing at his watch, he nodded toward the door. "Ten to four. Time to invite ourselves to tea with the Ambassador."