Jack needed no second bidding; he was only too anxious and eager to follow the direction of Rigby's outstretched finger. He was by no means lacking in the nerve and pluck which generally go to a young man of fine physique and clean habit. But there was something about the whole of this affair, a creeping suggestion of diabolical crime, such as one only encounters in the wildest realms of fiction.

And yet it seemed to Jack that his reading of the daily press recalled things just as vile in every-day life. With teeth clenched firmly, with a stern resolution to do nothing very likely to precipitate what might have been a terrible catastrophe, Jack looked into the room before him. As the door was half open and the two friends were hidden in the blackish shadow, it was possible to watch without the slightest chance of being seen.

For an empty house, dusty and gloomy and deserted as it was, the room in front of our two adventurers presented a striking contrast to the rest of the place. There was no window, or at least, where the window ought to have been, something in the way of an iron shutter stood, and over this a great wealth of silken hangings was artistically arranged. As to the rest of the apartment, the furniture was directly in keeping with the abode of a millionaire. Jack did not fail to notice the rich Persian carpet, the luxurious chairs and settees of the First Empire period, the fine pictures on the walls. The walls, too, had been recently decorated, so that there was not a single jarring note to mar the harmonious whole. There were flowers, too, grouped in the corners of the room and piled cunningly around the electrolier standing on the centre table.

"Now, that is a strange thing," Jack whispered. "So far as I could see, so far as I can see now, there is no sign whatever of the electric lighting in any other part of the house. Do you suppose that these people have taken this house in the ordinary way, or is it possible that----"

"Not a bit of it," Rigby replied. "They're not the sort of people to do anything as foolish as that. Nor would there be any occasion to go to the expense. Depend upon it, they know all about the character of the owner of this property, and that it is not in the least likely to let unless put thoroughly in order."

"Then, what about the electric light?" Jack suggested. "That would have to be put in by somebody. These people could not tap the main, or anything of that kind."

"There's a much simpler way than that, my dear fellow. Dr. Adamson lives next door, and I know perfectly well that he has electric light. It does not require much technical knowledge to wire a house, and anybody with a small amount of common sense could easily drill a small hole through a partition and attach a wire to one of the main lines next door. I think that explains the problem."

Jack had no further question to ask for the moment. His full attention now was concentrated on the occupants of the room. There were three of them altogether, two being dressed like superior mechanics, and were evidently there for some purpose connected with machinery. The third man, superior in every way to his companions, had his back turned to the door, so that it was impossible to get a glimpse of his features. He had in front of him an ingenious-looking arrangement, not unlike a magic lantern or a contrivance for throwing cinematograph pictures on a screen. At a sign from him, one of the workmen drew back the silken draperies covering what ought to have been the window, and a white sheet stood confessed.

"Give me the third slide by your left hand," the operator commanded. "That will do. Now switch out the light."

There was a click and a jerk, and immediately the whole room was plunged in darkness save for the fierce disc of blinding light that flashed upon the screen. Almost immediately a dazzling disc was transformed to the face of a man. Jack clutched at the arm of his companion.

"By heaven! do you see that?" he whispered. "It is nothing more nor less than the face of Nostalgo. Do you think this is merely a development of some novel form of advertisement, or is it possible that these fellows have hit upon some novel way of putting in posters?"

But Rigby had nothing to say. He was too deeply interested in the spectacle before him. It had occurred to him for the moment that there might have been something in what Jack suggested. It was just possible also that what he took to be a large sheet was no more than a wide stretch of paper.

At any rate, there was no hurry. There would be plenty of time to ascertain whether the supposed sheet on the wall was paper or not. Rigby had made no reply to Jack's cogent question, but he seemed to be quite as interested as his friend.

"Hang me if I know what to think of it," he said at length. "It seems to me as if these fellows were trying to work out something quite new in the way of lantern slides. Mind you, it is just possible that we are mistaken altogether in our assumption that Anstruther is carrying out some cunning rascality. These men may, after all, be no more or less than honest workmen."

"I can't quite see that point," Jack replied. "Honest workmen do not, as a rule, come in this furtive way to an empty house. Besides, look at them."

"That is all very well," Rigby argued. "But supposing that you were engaged upon some secret process which you did not want anybody to know anything about. And, besides, Anstruther is quite a genius in his way, and there is no reason why he should not be engaged upon inventing some new process of lithography."

"In that case," Jack said, "is it not a strange coincidence that they should be manufacturing these Nostalgo posters? I grant you that Anstruther is absolutely a genius, but his talents always take a sinister bent; in fact, I don't think the fellow could be honest if he tried. Still, we have plenty of time to find out."

"Do you really think that is paper?" Rigby asked. "It looks to me like it."

"It looks to me like it, too," Jack said; "but we shall have to possess our souls in patience."

"Hang me if I don't go and see," he said. "No, I don't see that there is any great danger unless they should happen to turn up the light again, and I do not suppose they will do that until the experiment is finished."

"For goodness' sake, do nothing rash," Jack implored. "From what we have already seen, we have to do with a gang who would not hesitate to cut our throats if it served their purpose."

The thing, after all, was not so hazardous as Jack had imagined. Just for an instant, as if by accident, one of the shaded electrics on the wall flashed out in a pin-point of diamond light.

"You clumsy fool!" growled the man behind the lantern. "What did you do that for? You might have spoilt all my work by your blundering folly."

The erring workman grunted out something in the way of an apology and a promise that he would be more careful in the future. Here, then, was Rigby's ............