"He will find that out for himself," said Beale.

"I wish him greater success than he has had," replied the other, and passed on, descending the stairs slowly.

Beale went back to his flat, passed to his bedroom and looked down into the street. He made a signal to a man at the corner and received an almost imperceptible answer. Then he returned to the two men.

"This fellow is too clever for us, I am afraid, and London with its tubes, its underground stations and taxi-cabs is a pretty difficult proposition."

"I suppose your man lost him in the tube," said McNorton.

"There are two ways down, the elevator and the stairs, and it is mighty difficult to follow a man unless you know which way he is going."

"But you were interrupted at an interesting moment. What are you going to tell us about the Green Rust?"

"I can only tell you this," said Beale, "that the Green Rust is the greatest conspiracy against the civilized world that has ever been hatched."

He looked sharply at Homo.

"Don't look at me," said the Parson, "I know nothing about it, unless----" He stopped and frowned. "The Green Rust," he repeated, "is that old man Heyler's secret?"

"He's in it," said Beale shortly.

"Is it a swindle of some kind?" asked the Parson curiously. "It never struck me that Heyler was that kind of man."

"There is no swindle in it so far as Heyler's concerned," said Beale, "it is something bigger than a swindle."

A telephone bell rang and he took up the receiver and listened, only interjecting a query or two. Then he hung up the instrument.

"It is as I thought," he said: "the doctor's slipped again. Had a car waiting for him in Oxford Street and when he saw there were no taxi-cabs about, jumped in and was driven eastward."

"Did you get the number of the car?" asked McNorton.

Beale smiled.

"That's not much use," he said, "he's probably got two or three number-plates."

He looked at his watch.

"I'll go along to Kingston," he said.

"I shan't be able to come with you," said McNorton, "I have a meeting with the commissioner at five."

"Before you go," remarked Beale, "you might put your signature to this declaration of my _bona fides_."

He laid on the table a blue foolscap blank.

"What's this?" asked the surprised McNorton, "an application for a special licence--are you going to be married?"

"I hope so," said the other cautiously.

"You don't seem very cheerful about it. I presume you want me to testify to the urgency of the case. I am probably perjuring myself." He signed his name with a flourish. "When are you getting the licence and what's the hurry?"

"I am getting the licence to-morrow," said Beale.

"And the lady's name is----?"

"I thought you had noticed it," smiled the other, deftly blotting and folding the form.

"Not Miss Cresswell?" demanded the police chief in surprise.

"Miss Cresswell it is."

"But I thought----"

"There are circumstances which may be brought to your official notice, McNorton," said the detective, "for the present it is necessary to keep my plan a secret."

"Has it anything to do with the Green Rust?" asked the other jokingly.

"A great deal to do with the Green Rust."

"Well, I'll get along," said McNorton. "I will telephone the Kingston police to give you all the assistance possible, but I am afraid you will learn nothing from the tramp till the morning, and perhaps not then."

He took his leave soon after.

"Now, Homo, it is up to you and me," said Beale. "You will have to keep close to me after to-morrow. Make yourself at home here until I come back."

"One moment," said Homo, as Beale rose and gathered up his hat and gloves to depart. "Before you go I want you to understand clearly that I am taking on this job because it offers me a chance that I haven't had since I fell from grace, if you will excuse the _cliche_."

"That I understand," said Beale.

"I may be doing you a very bad turn."

"I'll take that risk," said Beale.

"On your own head be it," said Homo, his hard face creased in a fleeting smile.

Beale's car was waiting, but his departure was unexpectedly delayed. As he passed down the stairs into the vestibule he saw a stranger standing near the door reading the enamelled name-plates affixed to the wall.

Something in his appearance arrested Beale. The man was well dressed in the sense that his clothes were new and well cut, but the pattern of the cloth, no less than the startling yellowness of the boots and that unmistakable sign-manual of the foreigner, the shape and colour of the cravat, stamped him as being neither American nor British.

"Can I be of any assistance?" asked Beale. "Are you looking for somebody?"

The visitor turned a pink face to him.

"You are very good," he said with the faint trace of an accent. "I understand that Doctor van Heerden lives here?"

"Yes, he lives here," said Beale, "but I am afraid he is not at home."

He thought it might be a patient or a summons to a patient.