To the constable who opened the cab door Foyle gave quick instructions in a low voice. The Princess Petrovska found herself ushered into a plainly furnished waiting room, decorated with half-a-dozen photographic enlargements of the portraits of high police officials and a photogravure of "Her Majesty the Baby." There the policeman left her.

Foyle came to her a moment later. His couple of questions to the cabman as he paid him had not been fruitful. He had been ordered by the lady to drive to Waterloo Station. It was a fairly obvious ruse, which would have had the effect of effectually confusing her trail, for from there she might have taken train, tube, omnibus, tram, or cab again to about any point in London.

"I am sorry," he apologised. "We shall have to keep you here for an hour or two while your statements are verified."

"I don't mind," she countered lightly. "It will be an amusing experience. I have never seen a police station before. Perhaps you would like to show me over while we're waiting, Mr. Foyle."

The superintendent was admiring her confidence a little ruefully. A pleasant-faced, buxom woman tapped at the door, and Lola eyed her with misgivings. Foyle's blue eyes were fixed on her face.

"I am afraid I must deny myself that pleasure," he said suavely. "There are other matters which will take up our time. First, I shall be obliged if you will let the matron here search you."

The nonchalance of the Princess Petrovska had disappeared in a flash, and Foyle noted her quick change of countenance. She had recollected she was carrying Lady Eileen Meredith's jewels. They would inevitably be found, if she were searched. She was not so much worried by what explanation she could give as to what would be the result of a questioning of Eileen. Angrily defiant, she was on her feet in a flash.

"You have no right to search me. I am not under arrest," she declared.

Foyle knew she was right. What he was doing was flagrantly unlawful unless he charged her with some offence. Yet there are times when it is necessary for a police officer to put a blind eye to the telescope and to do technically illegal things in order that justice may not be defeated. This he felt was one of the occasions. He ignored her protestations and left the room, closing the door after him. For a brief moment the woman forgot the breeding of the Princess Petrovska in the fiery passion of Lola the dancer. But if she meditated resistance, a second's reflection convinced her that it would be futile. The matron, for all her good-tempered face, was well developed muscularly, and did not seem the kind of woman to be trifled with. The Princess submitted with as good a grace as she could muster.

As the woman drew forth the casket of jewels Lola made one false move. She laid a slim-gloved hand on her arm.

"If you want to earn ten pounds you will give me that back," she said softly.

The matron shook her head with so resolute an expression that the word "twenty," which trembled on the Princess Petrovska's lips, was never uttered. Gathering in her hands the articles she had found, she stepped outside. In three minutes her place was taken by Foyle. He quietly returned to her everything but the jewel case. This he held between his fingers.

"Where did you get this?" he demanded. His voice was keyed to the stern, official tone he knew so well how to assume.

She gripped the side of a chair tightly.

"What is that to do with you? It is mine. Give it to me."

"Not unless you can prove it is yours. If you do not, I shall charge you with being in possession of property suspected to be stolen."

She bit her lips until the blood came. Her face had become very pale. If the threat were meant seriously—and she could see no reason why it should not be—she was in an awkward predicament. Ordinarily she had ready resource, a fertile genius for invention. Now her wits seemed to have deserted her. Cudgel her brains as she would, she could see no way out of the difficulty. To boldly state that the jewels had been entrusted to her by Eileen would involve opening up a fresh line of inquiry for the C.I.D. men that might have disastrous results. Nor was there any person who might bear out a story invented on the spur of the moment.

"Well?" He spoke coldly.

"I refuse to tell you where I got them," she retorted. "You must do as you like."

"Then it is my duty to warn you that anything you say may be used in evidence against you. You will be charged." He opened the door and cried down the corridor, "Reserve!" To the constable who answered he indicated the Princess by a nod. "Take this woman to the detention room. She will be paraded for identification in half an hour."

The detention room of a London police station is a compromise between the comparative luxury of a waiting-room and the harshness of a cell. Like a waiting-room it is furnished with chairs and tables, and like a cell its door is provided with a strong, self-acting lock. The Princess Petrovska gritted her teeth viciously as she was left alone, and paid no heed to the magazines and papers left on the table—a consideration for visitors that had not been discernible in the waiting-room.

Meanwhile, Foyle had set every available man of the divisional detachment of the C.I.D. busily at work. A couple had been sent to verify the account given by the woman of her movements on the night when the murder occurred. The remainder had been sent to bring in a score of women, the wives and daughters of inspectors and other senior officers.

Detective-Inspector Taylor had turned up with Wills, who was informed of the part he had to play.

"You say you couldn't recognise the woman who came out of Lord Burghley's house. Now we're going to give you another try. We don't want you to pick any one out unless you're absolutely sure. Mind that."

Some of the women who had been fetched in by the detectives were rejected by Foyle as being too unlike the Princess. He intended the identification test to be as fair as possible. The ten who finally took their places in the high-pitched charge room were as nearly like the Princess in build and dress as could be managed from the choice afforded. They stood in a row on the opposite side of the room from the steel-railed dock and the high desk. Then Lola was brought in. Her head was held high, and her lips curled superciliously as she took in the arrangements.

"Please choose a position among these ladies," said Foyle urbanely. "You may stand anywhere you like."

There was an angry glitter in her dark eyes as she obeyed. She was not the sort of woman to risk a scene uselessly. Then Wills was brought in. Foyle put a formal question to him.

"Have you seen any of these ladies before? Don't be in a hurry to answer. Walk down the line and take a good look at each."

Wills slowly carried out his instructions. As he reached the last woman he shook his head. Lola's eyes caught those of Foyle with a glance of malicious triumph. But the superintendent was not done yet.

"Walk round the room, if you please, ladies—from left to right. No, a little quicker. Now, Wills, see if you can recognise any of them by their walk."

Three times they made the circuit of the room, while the butler darted nervous glances from one to the other.

"It's no good, sir," he confessed at last. "I don't know any of 'em."

To Foyle the result was not unexpected. He had adopted the expedient as a forlorn chance of linking up the Princess with the crime. Now it had failed, he intended to try other measures. He dismissed Wills and the women with a nod of caution not to speak of the formality they had witnessed, and at a nod from him a uniformed inspector stood up by the high desk pen in hand.

"Do you charge this woman, Mr. Foyle?" he asked.

Taylor had ranged up against her, and almost unconsciously she found herself standing by the desk facing the officer.

She searched the superintendent's inflexible face to see if it gave any sign of relenting. Foyle was calm, inscrutable, business-like. That was what had struck her from the moment she entered the police station—the cool, business-like fashion in which these men had dealt with the situation. There were no histrionics. They might have been clerks engaged in some monotonous work for all the emotion they evinced. They treated her as impersonally as though she was a bale of goods about which there was some dispute.

She was not a person easily daunted, but the atmosphere chilled her.

She reflected quickly that her refusal to explain the possession of the jewels was playing into Heldon Foyle's hands. He would guess that they were Eileen Meredith's—in any case, she could not stop him from seeing and questioning the girl. What advantage would it be to be placed under lock and key? Before the superintendent could reply she had made up her mind.

"One moment. I can explain how I got the jewels if I can see Mr. Foyle alone."

The inspector looked hesitatingly at the superintendent, who was stroking his chin with his hand. Foyle murmured an assent and led the way back to the detention room. The woman swung round to him quickly once they were alone.

"Those jewels were entrusted to me for a particular purpose by Lady Eileen Meredith," she said peremptorily. "That is all you have any right to know. You can easily ring her up and ask her. Do it at once and let me go."

"Very well," he said imperturbably. "I shall keep you here until I have done so."

But it was not to Berkeley Square that he telephoned from the privacy of the divisional C.I.D. offices. It was to Scotland Yard. Within five minutes Chief Inspector Green was setting out from the great red-brick building to see, first, the Duke of Burghley and, secondly, Lady Eileen Meredith. A full hour passed away, and Foyle received the result of the inquiries into Petrovska's movements. Her alibi was complete. In every particular her story of her movements had proved right.

Green, arriving at the police station with an agitated and puzzled nobleman and his solicitor, saw his chief for a few moments alone.

"She admits having handed over the jewels to Lola, but she won't say a word beyond that," he said. "She's as obstinate as a mule. I have told the Duke something of where we stand, and he has agreed to take the gems back without letting her know. It was a tough job, but I got him to see at last that the girl might be implicating herself. He says he's never heard of Petrovska."

"H'm." Foyle rubbed his chin vigorously. "I'll have a talk with the old boy. See if you can get the Public Carriage Office to borrow us a taxicab, and get Poole to drive it slowly up and down this street. If she hails it when she goes out, well and good. If not, Bolt and you had better follow her, and the cab will come after you so that you can use it in emergency."

Green had done his work with the Duke and the lawyer with tact. Foyle found his interview with them confined to evading questions that he had no wish to answer. He dismissed them at last with the jewels in the custody of the man of the law. Then he went straight to his prisoner.

"You can go," he said abruptly. "I shall ask you to be very careful, however, Princess. If you are wise you will leave England at once."

"Why?" she asked, opening her blue eyes wide and gazing at him with blank astonishment.

His voice became silky.

"Because, my dear lady," he said, "I feel that your career in England may not be altogether without reproach. I shall try to find out a little more about it, and if I get a chance, I warn you frankly, I shall have you taken into custody. You are too mischievous to be allowed to run around loose."

Her red lips parted in a scornful smile.

"Oh, you make me tired," she retorted. "Good-bye, Mr. Foyle."

"Pardon me," he said, and thrusting a couple of fingers into his waistcoat pocket, fished out a piece of paper. "Do you know this writing?"

She handed the piece of paper back to him with a shake of the head.

"No. I never saw it before," she retorted, and passed out.

But Heldon Foyle had her finger-prints.