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 aesthetic. 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 Fraeulein 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 fr............