Turning to Joe: ‘Look – not sure I like this much, Joe. It’s . . . irregular. I’d rather deal with it myself. I’m not so quixotic as you – you’d jump in to save a dog! You go on back with Sir George. I’ll grab another taxi when I’ve found those two sluggards who ought to be here.’

‘No – I’ve a better idea,’ Joe replied. ‘I’m coming with you. But we’ll send George home as advance warning that we really are serious about supper. George!’ he shouted, opening the back door. ‘Slight change in arrangements. Something to check on down by the river. You carry on, will you? Jean-Philippe and I will be along in say – half an hour. Driver, take this gentleman to the address he will give you as soon as you’re under way.’

He banged peremptorily on the taxi roof to deny George a chance to argue and watched as the taxi made its way out of the courtyard.

They began to run along the Quai des Orfèvres towards the bow-shaped point of the city island beyond the Pont Neuf. A romantic spot, green and inviting and dotted with willow trees, it was a magnet for the youth of the city with proposals and declarations to make but also for the many drunken tramps who seemed to wash in and out with the tide. A hundred yards. Bonnefoye gave warning of their approach by tooting insistently on the police whistle he kept in his pocket. No duty officer came hurrying up to join them with tumbling apologies.

‘Why us?’ Bonnefoye spluttered. ‘A whole bloody building full of cops behind us and who’s rushing for a dip in this open sewer? We are. Must be nuts. Where are the beat men? I’ll have their badges in the morning!’

They paused to get their breath back on the Pont Neuf. The loveliest bridge, Joe thought, and certainly the oldest, it spanned the Seine in two arms, divided almost exactly by the square. Centuries ago it had been a stage as well as a thoroughfare and market place, a paved space free of mud where comedy troupes could perform. The Italian Pantaloon, the clown Tabarin, uselessly flourishing his wooden sword, had drawn the crowds with burlesque acts of buffoonery. In an echo of the rather sinister jollity, each rounded arch was graced with a stone-carved gargoyle at its centre, grinning out over the river. Joe and Bonnefoye added their own stony profiles to the scene as they peered over the parapet into the gloom, searching the oily surface of the fast-flowing water, the only illumination the reflections of the gas lamps along the quays and a full moon dipping flirtatiously in and out of the veils of mist rising up from the river.

‘Spring surge,’ said Bonnefoye. ‘Quite a current running. If anyone’s fallen in there, they’ll be halfway to Le Havre by now. Hopeless. Listen! What can you hear?’

‘Nothing.’

‘Exactly. No one here. Not even a clochard. At the first sign of trouble they’re off. So there has been some trouble, I’m thinking. Sod it!’

A strangled scream rang out from below in the park and to the right. Male? Female? Impossible to tell.

‘Here we go,’ groaned Bonnefoye. ‘I’ll go down and investigate. You stay up here and be spotter. Give me a shout the moment you see something.’ He clattered off down the stone staircase to the lower level, still tooting hopefully.

Left alone on the bridge, Joe clung with tense fingers to the stonework of the parapet, steadying himself. It always hit him like an attack of vertigo. A combination of height and the insecurity of seeing a dark body of water sliding, snakelike and treacherous, beneath his feet. He closed his eyes for a moment to regain control and heard Bonnefoye’s whistle cut off in mid-blast.

Joe looked anxiously to his left, aware of a slight movement along the bridge. A tall figure was approaching. He moved nearer, coming to a halt ten yards distant, under a lamp, deliberately showing himself. Dark-jawed, unsmiling, chin raised defiantly to the light, right hand in pocket. The Zouave. Waiting.

Angrily, Joe looked to his right to check his escape route and his second nightmare hit him with the force of a bolt of electricity. His body shook and he fought to catch his breath. A figure, also ten yards distant. Not so tall as the first but infinitely more terrifying. He could have been any gentleman returning from a show, shining silk top hat on his head, well-tailored evening dress, white waistcoat, diamond studs glittering in his cuffs. Urbane, reassuring, romantic even, until you noticed the black mask covering the upper half of his face. In a theatrical gesture, he raised his left hand, white-gloved, to cup his chin, looking speculatively at Joe. His right hand, ungloved, went up and slightly behind his back. Slowly enough to show the gleaming zarin it held.

Joe began to breathe fast, steadying his nerves. Two men. He didn’t fancy his chances much. He thought, on the whole, he’d go for the toff first. The leader. Though by the time he’d closed with him, the Zouave would have sunk his knife into his back. Take the Zouave first and the Fantômas figure would be ripping his throat out from behind. He remembered Dr Moulin’s hands in the morgue, clutching his hair, demonstrating the hold, and his skin crawled. That’s how it would happen.

No gun, he’d have to fight with his fists and feet. Then he remembered the doctor’s parting concern and his strange gift. He felt in his pocket, encountering the cold steel of the surgical instrument. Better than nothing and they wouldn’t be expecting it. These creatures only attacked the defenceless and the unready, he told himself. ‘It’s razor-sharp,’ the doctor had warned. But all Joe’s instinct was pushing him to explore, to handle his weapon. To decide – slashing or stabbing? Which would be the more effective? His safety – his life – depended on the quality of the steel implement. By the time he closed with his assailant, it would be too late to find out. Worth a cut thumb to be certain. And the quick flare of pain would jolt his senses fully awake. Tentatively he ran a thumb along the cutting blade. He repeated the gesture, more urgently, pressing his thumb down hard, the whole length of the cutting edge. And moaned in distress.

There was no edge. It was blunt. Not a scalpel. It was as much use to him as a fish knife. He held it in his hand anyway because he had nothing else. It would still glitter in the gaslight. It might fool them into thinking he was armed. And then, with a rush, with a flash of insight that came hours too late, he realized.

He could deceive no one. He was himself the fool. No mistake had been made when he was handed the useless tool. It was a stage prop. He was standing here, gaslit from both sides, at the stone prow of the island, framed up for his audience below, a modern-day Mr Punch. The only thing lacking was the cap and bells on his head and the hurdy-gurdy musical accompaniment.

Strangely, he felt a compulsion to play the part handed to him. To let them know that, however belatedly, he had worked it out. He held up the instrument before his eyes in a parody of a scene from Macbeth. ‘Is this a scalpel which I see before me?’ he mused. ‘Or could it be an earwax remover?’

He looked to the right again and saw the smile start in the masked eyes, the nod that acknowledged his moment of understanding. He looked to his left and the Zouave with panther stride began to close on him. He pushed the scalpel back into his trouser pocket, took a deep breath, put both hands on the parapet and vaulted over, leaping as far out into the void as he could manage, hoping he’d miss the built-up quayside and hit the water.

The cold of the spring surge waters knocked the breath from his body and he struggled to the surface gasping and choking. The stench of the river water was sickening. An open sewer, Bonnefoye had called it. He stared as a dead dog, bloated and disgusting, swept towards him and then bobbed away before it made contact. He struck out for the bank, glad enough to be carried by the current at an angle to the Pont Neuf, away from the two creatures on the bridge. He wasn’t a strong swimmer and his jacket was heavy with the weight of water, dragging him down. He spent a few moments treading water while he struggled out of it. Noises behind him. A gunshot rang out. He ducked under the surface and allowed himself to drift a few more yards.