When Beale left Krooman Mansions with his two companions he had only the haziest idea as to where he should begin his search. Perhaps the personal interest he had in his client, an interest revealed by the momentary panic into which her disappearance had thrown this usually collected young man, clouded his better judgment.

A vague discomfort possessed him and he paused irresolutely at the corner of the street. There was a chance that she might still be concealed in the building, but a greater chance that if he followed one of the three plans which were rapidly forming in his mind he might save the girl from whatever danger threatened her.

"You are perfectly sure you heard her voice?"

"Certain," replied Beale shortly, "just as I am sure that I smelt the ether."

"She may have been using it for some other purpose. Women put these drugs to all sorts of weird purposes, like cleaning gloves, and——"

"That may be," interrupted Beale, "but I wasn't mistaken about her voice. I am not subject to illusions of that kind."

He whistled. A man who had been lurking in the shadow of a building on the opposite side of the road crossed to him.

"Fenson," said Beale, "watch these flats. If you see a car drive up just go along and stand in front of the door. Don't let anybody enter that car or carry any bundle into that car until you are sure that Miss Cresswell is not one of the party or the bundle. If necessary you can pull a gun—I know it isn't done in law-abiding London," he smiled at Superintendent McNorton, "but I guess you've got to let me do a little law-breaking."

"Go all the way," said the superintendent easily.

"That will do, Fenson. You know Miss Cresswell?"

"Sure, sir," said the man, and melted back into the shadows.

"Where are you going now?" asked Kitson.

"I am going to interview a gentleman who will probably give me a great deal of information about van Heerden's other residences."

"Has he many?" asked Kitson, in surprise.

Beale nodded.

"He has been hiring buildings and houses for the past three months," he said quietly, "and he has been so clever that I will defy you to trace one of them. All his hiring has been done through various lawyers he has employed, and they are all taken in fictitious names."

"Do you know any of them?"

"Not one," said Beale, with a baffled little laugh, "didn't I tell you he's mighty clever? I got track of two of them but they were the only two where the sale didn't go through."

"What does he want houses for?"

"We shall learn one of these days," said Beale cryptically. "I can tell you something else, gentlemen, and this is more of a suspicion than a certainty, that there is not a crank scientist who has ever gone under through drink or crime in the whole of this country, aye, and America and France, too, that isn't working for him. And now, gentlemen, if you will excuse me——"

"You don't want any assistance?" asked the superintendent.

"I guess not," said Beale, with a smile, "I guess I can manage the Herr Professor."

* * * * *

On the south side of the River Thames is a congested and thickly populated area lying between the Waterloo and the Blackfriars Roads. Here old houses, which are gauntly picturesque because of their age, stand cheek-by-jowl with great blocks of model dwellings, which make up in utility all that they lack in beauty. Such dwelling-places have a double advantage. Their rent is low and they are close to the centre of London. Few of the houses are occupied by one family, and indeed it is the exception that one family rents in its entirety so much as a floor.

In a basement room in one of those houses sat two men as unlike one another as it is possible to conceive. The room itself was strangely tidy and bare of anything but the necessary furniture. A camp bed was under the window in such a position as to give its occupant a view of the ankles of those people who trod the pavement of the little street.

A faded cretonne curtain hid an inner and probably a smaller room where the elder of the men slept. They sat on either side of a table, a kerosene lamp placed exactly in the centre supplying light for their various occupations.

The elder of the two was bent forward over a microscope, his big hands adjusting the focus screw. Presently he would break off his work of observation and jot down a few notes in crabbed German characters. His big head, his squat body, his long ungainly arms, his pale face with its little wisp of beard, would have been recognized by Oliva Cresswell, for this was Professor Heyler—"the Herr Professor," as Beale called him.

The man sitting opposite was cast in a different mould. He was tall, spare, almost Æsthetic. The clean-shaven face, the well-moulded nose and chin hinted at a refinement which his shabby threadbare suit and his collarless shirt freakishly accentuated. Now and again he would raise his deep-set eyes from the book he was reading, survey the absorbed professor with a speculative glance and then return to his reading.

They had sat in silence for the greater part of an hour, when Beale's tap on the door brought the reader round with narrow eyes.

"Expecting a visitor, professor?" he asked in German.

"Nein, nein," rambled the old man, "who shall visit me? Ah yes"—he tapped his fat forefinger—"I remember, the FrÄulein was to call."

He got up and, shuffling to the door, slipped back the bolt and turned it. His face fell when he saw Beale, and the man at the table rose.

"Hope I am not disturbing you," said the detective. "I thought you lived alone."

He, too, spoke in the language which the professor understood best.

"That is a friend of mine," said old Heyler uncomfortably, "we live together. I did not think you knew my address."

"Introduce me," said the man at the table coolly.

The old professor looked dubiously from one to the other.

"It is my friend, Herr Homo."

"Herr Homo," repeated Beale, offering his hand, "my name is Beale."

Homo shot a keen glance at him.

"A split! or my criminal instincts fail me," he said, pleasantly enough.

"Split?" repeated Beale, puzzled.

"American I gather from your accent," said Mr. Homo; "pray sit down. 'Split' is the phrase employed by the criminal classes to describe a gentleman who in your country is known as a 'fly cop'!"

"Oh, a detective," smiled Beale. "No, in the sense you mean I am not a detective. At any rate, I have not come on business."

"So I gather," said the other, seating himself, "or you would have brought one of the 'busy fellows' with you. Here again you must pardon the slang but we call the detective the 'busy fellow' to distinguish him from the 'flattie,' who is the regular cop. Unless you should be under any misapprehension, Mr. Beale, it is my duty to tell you that I am a representative of the criminal classes, a fact which our learned friend," he nodded toward the distressed professor, "never ceases to deplore," and he smiled blandly.

They had dropped into English and the professor after waiting uncomfortably for the visitor to explain his business had dropped back to his work with a grunt.

"I am Parson Homo and this is my pied-À-terre. We professional criminals must have somewhere to go when we are not in prison, you know."

The voice was that of an educated man, its modulation, the confidence and the perfect poise of the speaker suggested the college man.

"So that you shall not be shocked by revelations I must tell you that I have just come out of prison. I am by way of being a professional burglar."

"I am not easily shocked," said Beale.

He glanced at the professor.

"I see," said Parson Homo, rising, "that I am de trop. Unfortunately I cannot go into the street without risking arrest. In this country, you know, there is a law which is called the Prevention of Crimes Act, which empowers the unemployed members of the constabulary who find time hanging on their hands to arrest known criminals on suspicion if they are seen out in questionable circumstances. And as all circumstances are questionable to the unimaginative 'flattie,' and his no less obtuse friend the 'split,' I will retire to the bedroom and stuff my ears with cotton-wool."

"You needn't," smiled Beale, "I guess the professor hasn't many secrets from you."

"Go on guessing, my ingenious friend," said the parson, smiling with his eyes, "my own secrets I am willing to reveal but—adios!"

He waved his hand and passed behind the cretonne curtain and the old man looked up from his instrument.

"It is the Donovan Leichmann body that I search for," he said solemnly; "there was a case of sleeping-sickness at the docks, and the Herr Professor of the Tropical School so kindly let me have a little blood for testing."

"Professor," said Beale, sitting down in the place which Parson Homo had vacated and leaning across the table, "are you still working for van Heerden?"

The old man rolled his big head from side to side in an agony of protest.

"Of the learned doctor I do not want to speak," he said, "to me he has been most kind. Consider, Herr Peale, I was starving in this country which hates Germans and regard as a mad old fool and an ugly old devil, and none helped me until the learned doctor discovered me. I am a German, yes. Yet I have no nationality, being absorbed in the larger brotherhood of science. As for me I am indifferent whether the Kaiser or the Socialists live in Potsdam, but I am loyal, Herr Peale, to all who help me. To you, also," he said hastily, "for you have been most kind, and once when in foolishness I went into a room where I ought not to have been you saved me from the police." He shrugged his massive shoulders again. "I am grateful, but must I not also be grateful to the learned doctor?"

"Tell me this, professor," said Beale, "where can I find the learned doctor to-night?"

"At his so-well-known laboratory, where else?" asked the professor.

"Where else?" repeated Beale.

The old man was silent.

"It is forbidden that I should speak," he said; "the Herr Doctor is engaged in a great experiment which will bring him fortune. If I betray his secrets he may be ruined. Such ingratitude, Herr Peale!"

There was a silence, the old professor, obviously distressed and ill at ease, looking anxiously at the younger man.

"Suppose I tell you that the Herr Doctor is engaged in a dangerous conspiracy," said Beale, "and that you yourself are running a considerable risk by assisting him?"

The big hands were outspread in despair.

"The Herr Doctor has many enemies," mumbled Heyler. "I can tell you nothing, Herr Peale."

"Tell me this," said Beale: "is there any place you know of where the doctor may have taken a lady—the young lady into whose room you went the night I found you?"

"A young lady?" The old man was obviously surprised. "No, no, Herr Peale, there is no place where a young lady could go. Ach! No!"

"Well," said Beale, after a pause, "I guess I can do no more with you, professor." He glanced round at the cretonne recess: "I won't inconvenience you any longer, Mr. Homo."

The curtains were pushed aside and the Æsthetic-looking man stepped out, the half-smile on his thin lips.

"I fear you have had a disappointing visit," he said pleasantly, "and it is on the tip of your tongue to ask me if I can help you. I will save you the trouble of asking—I can't."

Beale laughed.

"You are a bad thought-reader," he said. "I had no intention of asking you."

He nodded to the old man, and with another nod to his companion was turning when a rap came at the door. He saw the two men exchange glances and noted in the face of the professor a look of blank dismay. The knock was repeated impatiently.

"Permit me," said Beale, and stepped to the door.

"Wait, wait," stammered the professor, "if Mr. Peale will permit——"

He shuffled forward, but Beale had turned the latch and opened the door wide. Standing in the entrance was a girl whom he had no difficulty in recognizing as Hilda Glaum, sometime desk companion of Oliva Cresswell. His back was to the light and she did not recognize him.

"Why did you not open more quickly?" she asked in German, and swung the heavy bag she carried into the room, "every moment I thought I should be intercepted. Here is the bag. It will be called for to-morrow——"

It was then that she saw Beale for the first time and her face went white.

"Who—who are you?" she asked; then quickly, "I know you. You are the man Beale. The drunken man——"

She looked from him to the bag at her feet and to him again, then before he could divine her intention she had stooped and grasped the handle of the bag. Instantly all his attention was riveted upon that leather case and its secret. His hand shot out and gripped her arm, but she wrenched herself free. In doing so the bag was carried by the momentum of its release and was driven heavily against the wall. He heard a shivering crash as though a hundred little glasses had broken simultaneously.

Before he could reach the bag she snatched it up, leapt through the open door and slammed it to behind her. His hand was on the latch——

"Put 'em up, Mr. Beale, put 'em up," said a voice behind him. "Right above your head, Mr. Beale, where we can see them."

He turned slowly, his hands rising mechanically to face Parson Homo, who still sat at the table, but he had discarded his Greek book and was handling a business-like revolver, the muzzle of which covered the detective.

"Smells rotten, doesn't it?" said Homo pleasantly.

Beale, too, had sniffed the musty odour, and knew that it came from the bag the girl had wrenched from his grasp. It was the sickly scent of the Green Rust!