The setback seemed to act as a spur to Macadam. He remembered that he had a pal who was something of a dab hand at all things electrical. The pal was able to lend them a suitable rheostat of his own, which he set up in the department so that Macadam could operate the projector, and spark the electrical arc lamp that provided the illumination.

And so Macadam was able to show them the test footage he had got back from the processors.

They did what they could to turn the department into a kind of picture palace, draping Quinn’s trademark herringbone Ulster over the window to block out the light. It was only a partial success.

However, as the film began to ratchet through the escapement, Quinn felt the same anticipatory excitement – the sense that he was about to witness wonders and magic – that he always experienced when he went to a moving picture show. But as the seeping blurs of grey, white and black began to swoop across the glowing patch of wall, his excitement turned to bemusement. It was hard to tell exactly what he was seeing. Part of the frame was cut off in a block of heavy shade. The rest appeared to be out of focus.

The show was over in a matter of minutes, seconds even. There was an equal interval of deep, contemplative silence. Inchball broke it with a slow, sarcastic hand-clap.

‘There are one or two adjustments to be made,’ admitted Macadam as he removed Quinn’s Ulster from the window. It was a relief to get the light back. ‘I think I know what I have to do. The camera was not in the best position within the van. The lens was partially obscured. And I need to adjust the focus. I evidently made a mistake in calculating the depth of field. It’s all to be expected. Next time … next time, we’ll get it right.’

Quinn felt sorry for his sergeant and so mooted the possibility of setting up the camera in one of the boarded-up houses opposite. However, it turned out that the buildings were far from derelict. The occupants guarded their thresholds with all the jealous pride of suburban householders, but with a more suspicious and leaner glower. There could be no question of prevailing upon their public spiritedness or patriotism. Money might have bought access to a viewpoint, but the venality that allowed that also made them unreliable conspirators. They were just as likely to betray them to the Germans in return for a few bob.

And so Quinn had shifted the focus of the operation away from the shop on to the mysterious Hartmann himself.

He and Macadam took up positions on the Strand, on either side of the arch that led to the alley. Neither of them had seen Hartmann, but Inchball had repeated his incredulous description of the man so often that they felt sure they would recognize him. Should they see a large, bald, mustachioed man enter the passageway, Macadam would follow him in at a discreet distance and seek confirmation from Inchball, who would be in position on the other side.

Macadam’s spirits had rallied decisively when Quinn had held out the prospect of setting up the camera at whatever location they followed Hartmann to.

For Quinn, maintaining his concentration and enthusiasm proved harder. He continued to be visited by the image of Miss Dillard’s reproachful eyes. For example, once when he was looking into a ladies’ outfitters, he noticed that every one of the plaster dummies seemed to possess eyes of the same pewter grey, eyes that were not just like Miss Dillard’s; they were Miss Dillard’s. And every pair of those eyes was turned on him. If it was a sign that his conscience was troubling him, he could not think why. Or at least, why now, more than any other time. He had not spoken to her since the incident on the landing, over a week ago now. In fact, he had avoided all contact with any of his fellow lodgers. And so he had committed no new blunders. Her eyes had nothing fresh to hold against him, unless it was the very fact of his isolation that was the source of her reproach.

The weather continued to be changeable. Brief bursts of sunlight were quickly forgotten in the pervading damp gloom. The constant flow of traffic around them worked in their favour, creating an ever-changing population on the street. No one else was there for long enough to remark on the two men who never seemed to go anywhere. (Quinn took the precaution of flashing his warrant card at the local bobby, in order to forestall any unwanted enquiries from that quarter.)

They took it in turns to break, either to grab a hurried pie or a chop in a cheap restaurant on the Strand, or to take a leak in the public convenience in Fleet Street. The rest of the time they pretended interest in shop windows into which they barely glanced, Macadam because he had one eye on the entrance to the alley, Quinn because … well, it was enough to say his mind was usually elsewhere.

Herr Hartmann did not return to the shop. Dortmunder appeared to live over his shop, alone. When he pulled down the shutters in the evening, a light came on upstairs. As far as they could observe, he went out only to buy provisions from nearby shops. Not only did Hartmann not show, but there were no visitors to the shop at all, at least during the hours that they watched it. Apart from Inchball, who on Thursday afternoon put aside his disguise to return for another shave, Dortmunder did not have a single customer for three days. The incident with the van had clearly spooked Hartmann. Whatever operation he was running from the shop, it appeared to have been shut down. Their surveillance was effectively stalled.

And so, at the end of a fruitless, unrewarding week, Quinn called his officers in.

It was Friday morning. He stared at the wall, willing something to appear on its blank surface, a photograph, a diagram, anything that might give them a lead.

‘We have to look at this from a different angle,’ he said at last. As if to prove the point he turned his back on the wall and sat down at his desk. As it was, neither of his sergeants contradicted him.

Quinn looked down at the card lying on his desk.

You are cordially invited to the world premiere of

THE EYES OF THE BEHOLDER

‘The German community in London would naturally be interested in any cultural event which is connected to their country of birth. This film, for example. I would hazard a guess that Konrad Waechter, the man responsible for it, is a compatriot of theirs. Perhaps he is known to them.’

‘I should say so!’ Macadam sat up with sudden energy. ‘I have read about Waechter in the Kinematograph Enthusiast’s Weekly. His last film was very popular, I believe, and the new one is set to cause even more of a sensation. By Jove, sir! You have been invited to the premiere!’

Quinn’s gaze went to the end of the text on the card:

On Friday, April 17th 1914, at 7 p.m.

Before an audience of specially invited celebrities

‘The seventeenth. That is today. Perhaps I will go, after all. I will take Inchball with me so that he may look out for Hartmann. And Dortmunder too, for that matter.’

Macadam was crestfallen. Quinn couldn’t bear to see the enthusiasm knocked out of his sergeant. If Macadam was to be morose, then there was no hope at all.

‘Macadam, you may come along too, of course. We will get you in somehow. Now, you said you have read about this fellow, Waechter. May I see the article?’

Macadam’s expression lit up. With an eager bustle, he retrieved his collection of Kinematograph Enthusiast’s Weeklies from a drawer in his desk. A few moments of happy thumbing later, he spread out the article in question in front of Quinn. There was a photograph of a young man whose most distinguishing feature was the black patch over one eye. Though dressed in a vaguely bohemian fashion, his bearing seemed somewhat stiff and formal, his expression stern. This was in marked contrast with the rather foolish grin of the man whose hand he was photographed shaking. The second man was dressed ostentatiously in a flamboyant overcoat with astrakhan cuffs and collars. The caption read: Renowned Austrian director Konrad Waechter agrees two-week exclusive with Mr Porrick of Porrick’s Palaces for his new masterpiece, The Eyes of the Beholder.