There is no person in London easier to find than a cab-driver whose number is known, for the supervision of the Public Carriage Department is exhaustive. Yet, even so, it was some hours before the man Foyle sought was reported as being on his way to Scotland Yard.

He came at last, wonder and a little alarm in his face as he was brought into the room where the superintendent and Green sat. There are many rules the infringement of which will imperil a licence, and he was not quite sure that he might not have broken one.

Foyle motioned for the door to be shut. "So you're the cab-driver we're looking for, are you?" he said. "You're William White?"

"Yes, sir," answered the man. "That's my name."

"All right, White. There's nothing to be alarmed about. You picked up a lady outside the Metropolitan and Provincial Bank this morning. Just sit down and tell us where you took her."

"Oh, that is it?" said White, relieved to find that it was merely an inquiry and not an offence that he was called upon to answer for. "Yes, sir. I did pick up a lady there. I took her along to the General Post Office, and waited while she went in. Then——"

"Wait a minute," interrupted Foyle. "How long was she in there?"

"Ten minutes as near as a touch, according to the way the taximeter jumped while I was waiting. When she came out she asked me if I could take her to Kingston. I said yes. And she told me to stop on the Surrey side of Putney Bridge, because she expected to pick up a friend, sir. Well, he was waiting there for us——"

"What kind of a looking man was he?"

"A tough sort of customer. Dressed like a labouring chap. I thought it was a queer go, but it wasn't none of my business, and ladies take queer fancies at times. She didn't say nothing to him that I could hear, but just leaned out of the window and beckoned. He jumped in and off we went. We stopped at a tailor's shop in Kingston, and the man went in while the lady stayed in the cab."

"What was the name of the shop?"

"I didn't notice. I could show it to any one, though, if I went there again."

"Very well. Go on," said Foyle curtly.

"Well, in a matter of a couple of minutes out comes the chap again and spoke to the lady. She got out and paid me off. He went back into the shop and she walked away down the street."

"And that's the last you saw of them, I suppose?" asked the superintendent, with his left hand rubbing vigorously at his chin.

White shook his head. "No, sir. I went away and had a bit of grub before coming back. As I passed Kingston railway station, I saw the lady standing by a big motor-car, talking to the man seated at the wheel. I thought at first it was the chap I had driven down, but I could see it wasn't when I got a closer look at him. He was better dressed and held himself straighter."

"Ah! Could you describe him? Did you notice the number of the car?"

The driver scratched his head. "A sort of ordinary-looking man, sir. I didn't take much stock of him. The car was A1245—a big brown thing with an open body."

"Right you are, White," said Foyle with a nod of dismissal. "That will do for now. You go down and wait in the yard with your cab, and we'll get some one to go with you to Kingston. And keep your mouth shut about what you've told us."

When the door closed behind the man, his eyes met those of the chief detective-inspector. "You'll have to go to Kingston, Green. It's a hot scent there. You've got the numbers of the notes that Maxwell got from the bank. Find out if any of them were changed at the tailor's. They've taken precautions to blind the trail. What I think happened is, that she telephoned from the General Post Office to some motor-car firm to send a car from London to Kingston railway station, under the impression that it would be less risky. He went into the tailor's place to arrange for a change of clothes, and she dismissed the taxi as a measure of precaution. It was a piece of luck that the man noticed the motor-car, but we can't be absolutely certain of the number he gave. He had no particular reason to remember it. Anyway, I'll send it out to the county police, and ask them to keep their eyes open. Meanwhile, I'll set some men to work to see if any of the big garages have sent a car to Kingston, and get the number verified. If you 'phone me when you get down there, I'll let you know how things stand."

Green had his hand on the handle of the door, but suddenly something occurred to him. "Do you think she's gone with him, sir?"

Heldon Foyle made a little gesture of dissent. "I don't think it likely. It would double the danger of identification. But we can soon find if she's gone back to her home. I told Taylor, who is watching in Berkeley Square, to report when she returned." He touched a bell and put a question to the man who entered.

"Yes, sir," was the reply. "He rang up half an hour ago. You told me I wasn't to disturb you. He reported Lady Eileen Meredith had just gone in."

"There you are, then, Green," said Foyle. "That point's settled. You get along. I wish I could come with you, but it won't do for me to leave London just now, and goodness knows where you may have to finish up. Good-bye and good luck."

When Green had gone, Foyle gave a few instructions to cover the points that had arisen, and walked to Sir Hilary Thornton's room. The Assistant Commissioner looked up and proffered a cigar. "Think of the angels," he said. "I was just wondering how things were going."

"Things are straightening out a bit," said the superintendent. "It's been a busy day, and it's not over yet." And, puffing a ring of smoke into the air, he told in bare, unadorned fashion the events of the day. "It has been a narrow thing for Grell," he concluded. "Even now, I fancy we shall get him. Green's as tenacious as a bull-dog when he's got something to take hold of."

With his hands thrust deep in his trousers pockets, Sir Hilary strode to and fro across the room. "It's time we got a bit forward," he said. "The adjourned inquest will come on again soon, and we shan't be able to keep the question of identity up our sleeves any longer."

"There's a week yet," answered Foyle. "I don't think it will much matter what is revealed then."

The Assistant Commissioner came to a halt. "You're not a man to be over-confident, Foyle," he explained. "Do you feel pretty certain of having Grell under arrest by that time? I've not interfered with you hitherto, but for heaven's sake be careful. It won't do to make a mistake—especially with a man of Grell's standing."

Heldon Foyle lifted his shoulders deprecatingly. "It all depends upon an idea I have, sir. I am willing to take all responsibility."

"You're still convinced that Grell is guilty?"

"I am convinced that he knows all about the murder," answered Foyle ambiguously. "With the help of Pinkerton's, I've traced his history back for the last twenty-five years. He's had his hands in some queer episodes in his time before he became a millionaire. There are gaps which we can't fill up, of course, but we're pretty complete. There was one thing in his favour. Although he's known toughs in all corners of the world, he's never been mixed up in any dirty business. And as he's carried out one or two political missions for the United States, I suppose he's had to know some of these people. To-morrow or the next day, I expect to have the records of both Ivan Abramovitch and Condit. It will all help, though the bearing on the murder is perhaps indirect."

"You're talking in parables, like a detective out of a book," said Thornton, with a peevishness that his covering smile could not entirely conceal. "But I know you'll have your own way when you don't want to be too precise. How do you regard the burnt paper? Is it important?"

"It would have been if I could have saved it," said the detective regretfully. "As it is, it's of no use as evidence in a court, for it only rests on my word. I keep pegging away at it, but I'm not certain that I can fill it out as it should be. But you never know your luck in our trade. I remember a case of forgery once. The counterfoil of a tradesman's paying-in book showed £100 with which he was not credited in the books of the bank. The cashier was confident that his initials in blue pencil on the counterfoil were genuine. Yet he was equally certain that he had not received the money. The tradesman was certain that he had sent the money. There it was. I was at a dead end. One day, I noticed a little stationer's store near the tradesman's office. In the window were some blue pencils. I walked in and bought something, and casually remarked that I shouldn't have thought there was much demand for those pencils. 'Oh, schoolboys buy 'em,' said the old woman who served me. 'There's old ——s' son over the way. He buys half a dozen at a time.' Well, off I went to the grammar school that the boy was attending, and had a talk with one of the masters. He admitted that the lad was exceptionally clever at drawing. I was beginning to see my way, so had the boy called out of his class into a private room. 'Now, tell me, my boy,' I said, 'what did you do with the money you stole from your father on such and such a date?' The bluff worked. He turned pale, and then admitted that he had forged the initials, taken the money, and gone on a joy-jaunt for a week while he was supposed to be staying with an aunt. There was the luck of the idea coming in my head through looking at those pencils."

"Have you been looking at blue pencils to-day?" asked Thornton with interest.

"Something of the kind," admitted Foyle with a smile, and before he could be questioned further had vanished.

He had said nothing of the blotting-paper incident, for there were times when he wished to keep his own counsel even within the precincts of Scotland Yard itself. He did not wish to pin himself down until he was sure. In his own room, he unlocked the big safe that stood between the two windows, and taking out the roll he had abstracted from Lady Eileen's desk, surveyed it with a whimsical smile playing about the corners of his mouth. Once he held it to the mirror, and the word "Burghley" was plainly reflected.

"That ought to do," he murmured to himself, and, replacing it in the safe, swung the heavy door to.

The jig-saw puzzle to which he had likened criminal investigations was not so jumbled as it had been. One or two bits of the picture were beginning to stick together, though there were others that did not seem to have any points of junction. Foyle pulled out the dossier of the case, and again went over the evidence that had been collected. He knew it practically by heart, but one could never be too certain that nothing had been overlooked. He was so engaged when Mr. Fred Trevelyan was announced.

"Fred Trevelyan? Who is he?" he asked mechanically, his brain still striving with the problem he wished to elucidate.

"That's the name he gave, sir," answered the clerk, who ranked as a detective-sergeant. "I should call him Dutch Fred."

"Oh, I was wandering. Send him in."

There was nothing of the popular conception of the criminal about Freddy as he swaggered into the room, bearing a glossy silk hat of the latest fashionable shape on one arm. His morning coat was of faultless cut. His trousers were creased with precision. Grey spats covered his well-shone boots.

Foyle shook hands with him, and his blue eyes twinkled humorously. "On the war-path, I see, Freddy. Sit down. What's the game? Going to the big fight?"

The last remark was made with an object. Professional boxing attracts perhaps a larger number of the criminal fraternity than any other sport, except, possibly, horse-racing. In many cases, it is purely and simply love of the game that attracts. There is no ulterior motive. But in the case of Freddy, and men in his line, there was always the chance of combining pleasure with profit. The hint was not lost on the pick-pocket. A hurt expression crossed his face.

"No, Mr. Foyle," he declared earnestly. "I don't take any interest in boxing. I just called in to put you wise to something as I was passing."

"That's very nice of you, Freddy. What was it?"

The pick-pocket dropped his voice. "It's about Harry Goldenburg," he said. "I saw him to-day."

Foyle beat a tattoo on his desk with his fingers. "That so?" he said listlessly. "Out on the Portsmouth Road, I suppose?"

Dutch Fred sat up with a start. "Yes," he agreed, "just outside Kingston. How did you know?"

"Just a guess," laughed the superintendent. "Well, what about it? Did you speak to him?"

"I didn't have a chance," retorted Freddy. "I was in a little run-about with a pal when he came scooting by hell-for-leather. We only got a glimpse of him, and if he noticed us he made no sign. I thought you'd like to know, that's all. It was an open car, brown colour. I couldn't see the number for dust; it was A something."

"Well, we know all that," said Foyle. "All the same, Freddy, I am glad you dropped in: I won't forget it."

"Right oh, Mr. Foyle. Good evening." And the pick-pocket swaggered out, while Foyle thoughtfully stowed away his papers.

Some one brought in a cup of tea and some biscuits, and his watch showed him that it was a quarter to five. He had promised to call on Lady Eileen about six o'clock, and his mind dwelt on the potentialities of the interview as he lingered over his frugal meal. He had just poured out his second cup, when the telephone buzzer behind him jarred.

"A call from Liverpool, sir," said the man in the private exchange. "Mr. Blake wants you. Shall I put him through?"

A few minutes elapsed before Foyle heard the voice of the man who had been outwitted by the Princess Petrovska. "Is that Mr. Foyle? This is Blake speaking. We've got on the track of the lady again. She'd been staying at a boarding-house pretending she was a member of a theatrical company. A local man spotted her and came back to fetch me to make certain of her identity. But she must have got wind of it somehow, for she's hired a motor and slipped off. We're after her now. She's only got half an hour's start, and we've wired to have the main roads watched. I expect we'll have her in an hour or two."

The superintendent coughed. "Get along then, Blake. And don't smoke when you're on the job this time. Good-bye."

He replaced the receiver and returned to his neglected cup of tea. Things were evidently stirring. Was it altogether chance, he wondered, that Petrovska had chosen the day to make a move? Strange coincidences did happen at times, yet there was a possibility that her movements were correlated to those of Grell. Had the two managed to communicate? Well, at any rate he could rely on Blake and his assistants to find out whether she had received letters or messages. The matter was out of his hands, and it was not his habit to worry about affairs which he could not influence.