Two imposing stone lions flanked a pair of heavy, intricately carved oak doors beneath a sign in sharp Prussian lettering: Zutritt Verboten – Kaiserlicher Pavillon. Two sentries stood at flawless attention, their spiked Pickelhauben catching the dim station light.

David approached, pulled the Passierschein from his breast pocket and held it out toward the sentry, who had taken a step forward in challenge. The guard's eyes flicked from the document to David's immaculate tailored suitcoat. With a crisp click of his heels, he turned and unlocked the heavy iron latch.

As soon as David had stepped in, the door swung shut, cutting off the screeching locomotive brakes and the shouting of officers on the platforms. The silence inside was heavy, absolute, and thick with the smell of floor wax and stale pipe tobacco.

An adjutant in a pristine uniform bowed politely. "Herr Meyer, Der Kronprinz ... The Crown Prince is engaged in briefings on the tracks. You are requested to wait here until your escort arrives."

David nodded and followed the adjutant into a huge room. "This is Salon Charlemagne, and you will find much here to occupy your eyes." He stopped and pointed. "This shows Emperor Charlemagne, seated on his throne in Aachen, a magnificent window commissioned by His Imperial Highness, Kaiser Wilhelm."

After David thanked him, the adjutant left, leaving him completely alone in the vast room. He set his bag and case down and took a slow, deliberate breath, ensuring his posture remained relaxed, remembering the see-through mirrors of the interrogation room in Karlsruhe.

Shuddering at the memory, he walked to the centre of the salon, his boots silent against the thick Persian rugs. Then turning, he examined the massive stained-glass window towering above him. The shaded afternoon light filtered through the glass, casting a multi-colored glow across the floor.

As he examined it, he realised this was the sense of power Wilhelm would have grown up with. An absolute right to rule. The privilege of birth, not of ability. But to sustain it, why resort to war? Why not prosper together?

He turned away, crossed the room and sat facing the fire crackling in the massive stone hearth. Above the mantel hung a framed portrait of the Kaiser, staring down with cold, autocratic eyes. The attitude. Need to find a softness beneath it. Relax and remain open. He might follow as he did in Worms and Karlsruhe.

Leaning back in the chair, he closed his eyes and reviewed the previous interactions.

A long while later, he heard the faint, muffled footsteps on the rugs and opened his eyes as an officer approached and said, "The Crown Prince is ready to receive you." Then, gesturing for two soldiers to take his suitbag and sample case, he added, "Follow me, please."

They bypassed the crowded civilian platforms and walked into the restricted military sector of the yard. Steam hissed, locomotives chuffed, and brakes squealed, seemingly on all sides. Endless lines of munitions cars stretched out into the grey afternoon, and David realised the scale of Metz as a logistical hub.

At the far end of a heavily guarded siding, isolated from the soot of the main tracks, sat a locomotive attached to a single, deep-blue carriage. Its polished brass fittings gleamed even under the overcast sky, and the Hohenzollern crest was embossed in gold on its flank. Sentries with fixed bayonets stood at stiff attention beside the steps.

The officer led David up the iron stairs, opened the door, ushered him in and had the soldiers place the bag and case on the bench. The moment the heavy mahogany door clicked shut behind them, the industrial roar of the Metz railyards died, giving way to a surreal, opulent silence.

The air inside the private railcar smelled of expensive beeswax and rich Havana cigar smoke. Oriental rugs overlapped on the floor, and polished walnut panelling lined the walls, reflecting the soft glow of electric sconces. At the far end of the salon, stretched out on a plush green silk sofa with a bottle of wine in an ice bucket, was Crown Prince Wilhelm.

"Ah, the watchmaker from Bienne!" Wilhelm called out, laughing as he tossed a sheaf of papers onto a side table. He didn't look like a man commanding a bloody siege; his tunic was unbuttoned at the neck, and his slim, rakish frame radiated the bored energy of a dilettante on holiday. "Tell me, David, did you bring the Yquem, or must I resort to Champagne again today?"

"The wines are in my bag, Your Imperial Highness," David said, stepping forward with a practised smile, his eyes casually sweeping the room, spotting a large, heavily marked operational map pinned to the wall behind the Prince. "But, you might wish to taste a robust dry white first, a Weißburgunder from my great-aunt's Schaffhausen estate."

"So, you were also unable to find any Yquem."

"To the contrary, sir. I found a selection of ten vintages, and acquired two of each for you, including one to test our memories of the 1893 Steinberger Eiswein."

Now closer to Wilhelm, David realised that he looked a decade older than he had in Worms and Karlsruhe. His eyes had lost their former brightness and royal arrogance and were bloodshot and hollow. "But the Yquem is better tasted cooler than the Weißburgunder – and besides, the drier wants tasting first."

"Fine, then." He sat up and removed the Champagne from the ice bucket. "Place the two in here."

David returned to his suitbag, unbuckled it, removed the two boxes and carried them along to Wilhelm's table. "Because of the time constraint, the weight, and the travelling restrictions, I brought only five vintages of the Yquem."

"And the others are to follow by freight."

"No, they are far too fragile for that. Besides, I imagined some overly zealous border agent thinking they were unstable nitroglycerine and ordering them destroyed. It would be better for me to send a private courier or come again myself."

Wilhelm pursed his lips and nodded while David opened the boxes, took out two bottles and placed them in the ice bucket. "You may wish to examine the watch samples while these chill."

"Yes, the watches. But, tell me, David, how have you found these wines when my agents repeatedly failed?"

David shrugged, and as he walked along the salon to fetch the sample case, he said, "Knowing the market. Knowing where to look."

He returned, opened the Rolex case and set it in front of Wilhelm. "These are the three latest ladies' models, each in chromium-steel, silver and gold. Because of their size, they are not as precise as men's chronometers, but they are considered the most accurate watches available for women."

Wilhelm examined them in silence for a while, lifting and turning, then he said, "The same exquisite craftsmanship. Might I buy three of each in gold? Let them pick their favourites. You could bring them with the other Yquem vintages."

"Yes, we can do that." Great! Another meeting. Now to use this one. "Have your officers found the Rolex precision useful?"

"Very much so. Coordinating the artillery barrages with troop advances allows us great advantage at Verdun."

"As we suspected in Switzerland, sir. The watchmakers talk of the German precision their watches allowed in February."

Wilhelm pulled back his left cuff, revealing his gold watch. "And still allow. Last week, our artillery barrages at Fort Vaux were timed to the exact second." He paused and stared at the ticking second hand. "But what is the use of perfect timing when the High Command is blind? We took the fort, but for what? Falkenhayn has lost his nerve – or his mind."

David nodded, remaining silent for a while, then said, "On my way here, I noted railcars loaded with artillery pieces, troops moving northward. It appears he is now reinforcing the position."

Wilhelm's face darkened. "Not to reinforce, but to starve. Yesterday, Knobelsdorff brought me draft transfer orders." He hissed the last word. "He wants to pull a corps and several of my best heavy batteries away from Verdun – send them north-west, toward the Somme, toward Bapaume. All on rumours that the English are massing there."

He slammed his fist on the mahogany table. "They talk of rebalancing the Front as if it were an abacus. Knobelsdorff writes the orders, shows them to Falkenhayn, and only then lays them before me as decisions already made. I am told, not consulted. They treat me like a ghost – in my own headquarters!"

David recognised the tirade was more than only injured pride – a fissure in the German will. Verdun to be thinned for something new along the Somme. A corps and heavy batteries marked for Bapaume. The rails, the staff movements, and now this anger – together they began giving clear shape to a threat along the Somme. The details are for London to fill in.

He allowed Wilhelhem's anger to settle a bit, then nodded toward the ice bucket. "Shall we move to more pleasant matters, sir? The Weißburgunder should now be at a complementary temperature."