Yusupov studied the horizon once more, trying to discern the lights of the approaching town. He was twenty-three, and had already felt the hand of death close over him. He prayed that Casparov would be waiting at the bridge, that he had found a way of evading their pursuer. It was essential for them to find a hiding place for the casket in Pokrovskoye.

'Perhaps we are safe now,' said Dmitry as the sleigh turned toward the smoking chimneys of the town. 'May we have the strength to do what must be done.'

'Our story begins in the reign of Tsar Nicholas II, in the year 1908,' said Dr Harold Masters, studying his disinterested students as they lolled in their seats. 'Starving Bolsheviks fled across Russia with a precious cargo; a jewelled casket fashioned by Karl Fabergé and stolen from Rasputin himself, its contents unknown – and yet the men in the sleigh were willing to die to preserve it. Their flight from Rasputin's secret shrine at St Petersburg was doomed, but before they were brutally murdered in mysterious circumstances, we know that the casket was passed on, to make its way in time to New York.

'In the late 1920s a family of wealthy Franco-Russian emigrants who had escaped to America on the eve of the October revolution sailed on the SS Brittanique to Liverpool. The ship's passenger inventory tells us that the jewel-box was in their possession then, listed as inherited family property. But following the tragedy on board their ship…'

The sun had set an hour ago, but the sea was still blacker than the sky. Alexandrovich Novikov stood watching the churning wake of the ship with his gloved left hand clasping the wooden railing. Powerful turbines throbbed far beneath his feet, and he rode the waves, balancing as the liner crested the rolling swell of the sea. Back in the state room his wife, his brother and his children chattered excitedly about their new life in England, trying to imagine what, for them, was quite unimaginable. They would have new names, he had decided, European names that others would be able to pronounce without difficulty. They were being given a second chance, and this time the family would prosper and grow. There remained but one task for him to accomplish; the removal of the final obstacle to their safety. He reached inside his coat and withdrew the Fabergé casket. The value of the jewelled casing meant nothing to him, for its loss was but a small price to pay for the safe-keeping of his family.

He weighed it in his hand, worried that the rising wind might catch and smash it against the side of the ship. He had drawn back his arm, ready to hurl it into the tumbling foam below, when someone snatched at his coat-tails, spinning him around and causing him to lose balance on the tilting wet deck. Before he could draw breath, the stars filled his vision and he saw the railing pass beneath his legs, then the great black steel side of the ship, as the sound of the monstrous churning propellers pounded up around him.

Sinking into the ocean, Alexandrovich Novikov was dragged under by the great spinning blades and cleft in two, the pieces of his body lost forever in the frothing white foam. On the deck he had left, the unthrown casket slid beneath a stairwell with the rolling of the ship and was retrieved by a passing steward, whereupon the alarm was raised and a frantic search begun for its missing owner.

'And so we arrive in London,' continued Dr Masters. 'The bereaved Franco-Russian family who moved there from Liverpool in 1928 planned to build property in the city – but their assets were badly damaged in the financial crash of the following year. The headquarters of their empire, a magnificent building on the north bank of the Thames designed by the great Lubetkin, went unfinished. Here, the trail of Rasputin's jewelled box finally goes cold. We have to presume that it was sold off to the owner of a private collection as the family fought debts and a series of appalling personal tragedies…'

The building beside the old Billingsgate Market had never been properly finished, and now its poorly set foundations had been pulled up to clear the site and make way for a new Japanese banking syndicate. It was during the third month of digging, just prior to the new concrete foundations being poured into their moulds that the little casket, wrapped in an oilskin cloth and several layers of mildewed woven straw, was unearthed. The find was briefly mentioned on the six o'clock news that night, and excited speculation from experts about what might be discovered inside.

Before the box could be opened, however, it was sent to the British Museum to be cleaned and X-rayed. From the ornamentation of an exposed corner section of the casing it was already assumed to have been manufactured by a Russian jeweller, possibly the great Fabergé himself, which made it extremely valuable and placed it in the ownership of the royal court of Tsar Nicholas. It was, perhaps, too early to hope that the box might contain documents pertaining to that fascinating, tragic family.

The casket was entrusted to an unlikely recipient, a twenty-seven-year-old woman named Amy Dale who worked at the museum. In usual circumstances such a high-profile find would have been offered for examination to one of the more experienced senior staff, but Amy was having an affair with a hypertense married man named Miles Bernardier who functioned as the present director of the excavation, and Miles was able to take a procedural short cut that allowed him to assign the find himself. This was not as dishonest as it sounds, for Amy was fast becoming recognised as a luminary in her field, and as her own department head was overseas for two months advising at an excavation in Saudi Arabia, the pleasurable task of uncovering the casket's secrets fell to her.

The night before Amy was due to have the casket X-rayed, a supposedly psychic friend from the Mediterranean ceramics department seized her hands in the Museum Tavern and warned her that something strange was about to happen in her life. She pushed a hand through her frizzy blonde hair, laughing off his prediction, and ordered up another round of drinks. While they drank and chatted, the mud-encrusted casket, sealed in a large ziploc bag, sat in a basement vault of the British Museum waiting for its secrets to be exposed to the light.

The sun was scorching down in a sapphire sky the morning Spanky came back to town. The wind had changed direction, from the faintest breeze drifting down across the south to a fierce fresh blast that stifled the surface of the Thames and brushed against pedestrians in the Strand, ruffling them like hair being combed the wrong way.

Balancing delicately as he placed one patent black Church's Oxford-toecapped shoe after the other, Spanky walked along the electrified third rail of the London, Chatham & Dover Railway, crossed the bridge over the river into Cannon Street station and carefully sniffed the air. Beneath the fumes of the choked city, behind the oil of machinery and ozone crackle of electricity, beyond the perfumes and deodorants and the smell of warm working flesh, he caught the faintest tang of enamel and oilskin, wolf urine and sea-brine and city soil. It was quite enough to tell him that the object of his search was within a five-mile radius.

On the station platform he almost melted into the crowd, just another devilishly handsome young man arriving in the teeming city with an unrevealed agenda. Spanky's purpose, though, was single and specific; to locate the casket currently residing in the vault at Amy Dale's department.

A smile teased those who caught his eye; he permitted himself that. He could afford to be happy, for the battle was already half-won. He had seen the girl on television, speaking nervously into a microphone, pointing back at a great hole in the ground. The network had even taken the trouble to label her for him, displaying her name and place of employment. It only remained for him to meet with the girl and explain, in calm and rational tones, that he needed her to give back what was rightfully his.