'I'll have the irons off him as soon as we're under way again,' Captain King remarked as, round about sunset, they came in sight of what had once been the ancient port of Heraclea on the Sea of Marmara. That'll make it the easiest thing in the world for him to leave us. Although, you never know. We may be imagining things – painting your two admirers blacker than they are.'

'It's still wise to be prepared,' Marianne replied. 'I can't thank you enough, Sir James.'

Thus it was with a more tranquil eye that she watched the two Englishmen go ashore, amid a welter of baggage slung over the side and the shouts of the boatmen and porters hired to transport them from the three-decker, by means of a caique, to the waterfront, where a bustling, cheerful crowd was welcoming the cool of the evening.

Cockerell and Foster quitted the ship without a word of thanks or farewell, and for a long time their green sunshades could be seen bobbing on a sea of turbans and felt hats. They vanished at last into the compact mass of brightly coloured houses and mosques, riding jerkily on donkeys and surrounded by guides armed with staves and by an eager, screaming throng of small boys.

'The ingratitude of it!' Marianne said. They didn't even say good-bye to you. After all you've done for them!'

But Sir James only laughed and gave the order to weigh anchor. The Jason heeled over gracefully, almost as though relieved of a disagreeable burden, and resumed her course, while the setting sun turned the sea to amethyst and silvery dolphins played about the golden islets.

This was the last stage. The long exhausting voyage, which had so nearly cost Marianne her life on so many occasions, was drawing to an end. Constantinople was a bare thirty miles away now, and she was half-amazed to think it could be so near.

Gradually, in the dire days that had passed, the city of the golden-haired sultana, from whom she had hoped for so much, and most of all a reason to hope, had come to seem to her like a mirage, a kind of legendary city, eternally receding from her into time and space. Yet now that harbour lay close at hand. The numbers of sails that studded the darkening sea bore witness to it, as did the lighter trails in the deep blue of the sky, already velvety with oncoming night.

Later that evening, when the wind had dropped suddenly and the ship sailed on under slackened canvas, sliding with a silken rustle through the calm waters, Marianne stood on deck and gazed at the stars of an oriental night that was as balmy as anything she had imagined in the days when the future was still inscribed for her with the name 'Jason Beaufort'. Where was he at that moment? What seas was he sailing in his pride or his grief? Where was the Sea Witch spreading her white sails, and whose hand was at the helm? Was he still living somewhere on the face of this earth, the man who only yesterday had claimed in his pride and mastery that there were two things only in this world he loved, the woman he had won only to lose and the ship that bore the likeness of her face.

On that last night of wandering, the onslaught of regrets grew ever more determined. She had trodden a long and painful road to reach the city whose nearness she could now sense, with the aim of doing her utmost to recall its heart – a fragile heart because it beat in a woman's breast, however ardent – to its 300-year-old alliance with France. She had shed on the way all that was true and real in her life: love, friendship, self-respect, fortune, even her clothes, to say nothing of the husband she had never even seen, murdered by the hand of a madman. Would there ever be a harvest? Would she at least return to France with the old alliance renewed? Or would there be failure there also, to match the private tragedy that still lurked in her womb, clinging with such tenacity that nothing, it seemed, could dislodge it?

She remained there for a long time, watching the big bright stars and searching for some sign of hope or encouragement. One in particular seemed to glow more bright and then fell away from the blue vault and plunged like a miniature meteor to extinction.

Marianne crossed herself, hurriedly, and with her eyes fixed on the point where the star had disappeared, murmured the traditional wish into the evening air.

'Let me see him, Lord! Let me see him again, whatever the cost! If he is still alive, let me see him again, just once…'

That Jason was still alive, in her heart of hearts, she did not doubt. In spite of the cruel way he had treated her, in spite of his raging jealousy and a manner so strange that she had come to wonder if Leighton had not been feeding him secretly with some drug to induce a murderous and frenzied state, she knew that he was too deeply embedded in her heart for her to tear him out without destroying herself; and that even if he were at the other end of the earth, his life could not cease without her being in some way aware of it, through the mysterious vibrations of the soul.

The capital of the Ottoman Empire came in sight just at sunrise. At first it was no more than an outline, seen through a silvery haze on the distant skyline over the pearly sea, made up of nebulous domes and the faint spires of minarets.

On the Asian side the dark green hills, dotted with white villages, tumbled into a sea thick with shipping that looked as if it might have come straight out of some eastern tale: dark brown mahones, driven by the powerful arms of colourfully-dressed oarsmen; caiques gilded and painted like odalisques; shark-nosed xebecs, red and black; antiquated galleys with their long sweeps lying parallel on the surface, like gigantic water beetles; chektirmes, with angular, skyward-pointing sails – all converging on that unreal city shimmering in the sunlight.

Slowly it grew, until the entire city was spread out before them, flowing away from the ochre-coloured walls strung out between the fortress of the Seven Towers, past the Seven Hills and the Seven Mosques, like the arches of some titanic bridge, all the way to the black cypresses of Seraglio Point, in an astonishing jumble of red roofs, translucent domes, gardens and ruins of antiquity, like mighty shoulders braced at the critical moment to prevent the whole edifice of white cupolas ranged between the six minarets of the mosque of Ahmed and the great buttresses of St Sophia from rushing headlong into the sea.

As they rounded the Princes' Island they could see the crenellated line of the sea-wall, and the iridescent pearl began to take on a more precise definition.

The great ship curtsied daintily, her tall white sails dipping to the morning breeze as she came round Seraglio Point and entered the Golden Horn.

This was the great crossroads of the sea, where the hubbub of old Europe met the silence of Asia. The majesty of this threefold city was overwhelming. It was like stepping into some Ali Baba's cave: your eyes were blinded by the light and brilliance of it all so that you did not know where to look or what to wonder at the most. Then, in the same instant, the sheer seething life of this melting pot of all civilizations took you by the throat and left you helpless.

Clinging to the quarterdeck rail beside Sir James, who was taking it all in with worldly, unastonished eyes, Marianne stared about her at the vast, pullulating harbour like a blue tongue poked in between two different worlds.

To the left were the colourful, picturesque ships of the Ottoman Empire, tied up to the quays of Stamboul. Facing them, at the Galata moorings, were the ranked vessels from the west: black Genoese, Dutch and English, the multicoloured pennons decking their bare yards like so much fruit left unpicked by a careless gardener.

On either shore swarmed the busy crowds who, directly or indirectly, won their livelihood from the sea: seamen, customs-men, brokers, scribes, agents of merchants or foreign embassies, porters, stevedores, tradesmen and shopkeepers, and, everywhere, the tall felt hats and military figures of the janissaries of the port police.

Boatloads of men tugged furiously at the sweeps to tow the three-decker ponderously to her anchorage. At the same moment, a barge manned by hard-hatted English seamen put out from the shore and came to meet her. Upright in the stern was a very tall, thin, fair man, dressed with immense elegance. His arms were folded on his chest, and a flowing, light-coloured cloak blew about him.

At the sight of him, Sir James gave a start of surprise.

'Well, God bless my soul! It's the ambassador!'

Marianne was startled out of her own contemplation.

'What?'

'It would seem, my dear, that our two troublemakers must have rather more influence than we thought. The man in that barge is Stratford Canning.'

'Are you trying to tell me he is coming here in person to arrest a poor devil of a Greek who so far forgot himself as to try and choke the life out of a measly architect?'

'It hardly seems likely on the face of it but – Mr Spencer!' The lieutenant appeared at his side. 'Be so good as to ask the midshipman of the watch to step down to the cable tier and cast his eye over it. If the prisoner's still there, heave him out of a gun-port if you must, only get him off this ship. Or I won't answer for the consequences. I trust his irons have been properly filed through?'

The young man smiled. 'No need to fret about that, sir. Saw to it myself.'

'Then all that remains for us to do,' the captain observed, surreptitiously mopping his brow with his handkerchief, 'is to greet his excellency. No, don't you run away, my dear,' he added, as Marianne made a movement to withdraw. 'I'd rather keep you with me. I may need you. He's seen you, in any event.'