With his mind revolving the strength and weakness of his theory, Heldon Foyle returned to Scotland Yard. He paused for a moment at the door of the night-inspector's room.

"Anything for me, Slack?" he asked. "Has Mr. Bolt come in? Ah, there you are, Bolt. Come down to my room." He led the way down the green corridor, the divisional inspector following.

"Well?" asked the superintendent sharply, as he seated himself in his office.

"I have seen the manager, a hall-porter and a chamber-maid at the Palatial, sir. They repeat what they said in their statements before. The Princess left the hotel at about ten o'clock. No one can fix the time precisely, but it was certainly not before ten. She made up her mind very suddenly, the manager tells me."

Foyle was rummaging with some papers. "Thanks very much, Bolt. Stand by in case I want you. Tell Slack if he hears from Mr. Green to ask him to leave things and come up to me."

He concentrated himself on the neat bundle of documents in front of him, and gave his mind with complete detachment to the study of several of them. The investigation had narrowed itself. Whoever was guilty was in his hands. The choice lay between Robert Grell, Lady Eileen Meredith, and the Princess Petrovska.

The reconstruction of the crime for the benefit of the Assistant Commissioner, Foyle had purposely made provisional, but he was becoming more than ever convinced in his own mind that, in spite of appearances, Lola was the person at the bottom of the matter. She had left the Palatial about ten. If, he argued, she had left Grosvenor Gardens immediately after the murder it would have been possible for her to get to the Palatial by that time and to immediately make arrangements to leave. But for all that his intuition told him he was right, he could see no way of fixing the guilt on her.

He placed the dossier back in a drawer and, lighting a cigar, paced up and down the room puffing furiously. Half an hour after midnight Green came in.

"Yes, it's worth trying," soliloquised Foyle aloud.

"What is, sir?" asked the chief inspector, stopping with his hand on the door-handle.

"Ah, Green. I was just thinking aloud. Everything all right in Berkeley Square?"

"Everything quiet, sir."

"Well, things have been happening since I last saw you. I want your opinion. Sit down and listen to this."

Green selected a comfortable arm-chair by the desk, while the superintendent went over his interview with Grell. The chief inspector made no comments until the story was finished. Then he sat in silent thought for a while.

"I've got faith in your idea, sir," he admitted at last. "It's likely to be right as anything. But I am doubtful if we shall be able to get any admission from the Princess."

"One never knows," retorted Foyle. "She's not under arrest yet—only detained. We're entitled to ask her questions to see if she can clear herself. But our best chance is to take her off her guard. We might go along and wake her out of her sleep now and chance it."

The Princess Petrovska had been allotted a couch in the matron's room of Malchester Row police station, partly to spare her the ignominy of a cell, partly to ensure that she should be under constant supervision. Her sleep was troubled, and she woke with a start when the matron roused her.

"You must dress at once. Some gentlemen are waiting to see you."

"Waiting to see me? Who are they?" she asked. Her nerves were still quivering, but her voice was steady and her face composed.

The matron had received her instructions. "I don't know who they are," she replied, in a tone that did not invite further questioning.

Lola, for all her iron will, found her mind dealing with all sorts of possibilities as she dressed herself mechanically. It was not for nothing that Foyle had chosen that hour for his visit. The sudden summons at such an hour, amid unusual surroundings and the speculation as to what it would be for, had upset the woman's balance.

She was taken by the matron into the same room where Grell had been questioned an hour before. Foyle and Green sat at the table and, to her imagination, there was something of judges in their attitude. A chair had been placed at the other side of the table facing them, and the lights were so arranged that while her face would be fully illuminated, theirs would remain in the shadow.

"Sit down, will you," said Foyle suavely, when the matron had gone, closing the door behind her. "We're sorry to trouble you at this hour, but matters of urgency have arisen."

She strove to read their faces as she seated herself, but the light baffled her. "I am quite at your disposal, Mr. Foyle," she said, hiding her uneasiness under an appearance of flippancy. "What do you want?"

The superintendent balanced a pen between his fingers. "Mr. Green has already explained that you are not under arrest," he said, in a quiet, cold voice. "We are detaining you. Whether you will be the subject of a grave charge depends upon your answers to the questions we shall put to you. You must clearly understand, however, that you are not bound to answer."

"That sounds serious," she laughed. "Go on, Mr. Foyle. Put your questions."

"Very well. Do you still deny that you visited Mr. Grell's house on the night that the murder took place? I think it fair to tell you that we have had statements both from Ivan Abramovitch and Mr. Grell that you were there."

He eyed her sternly. She made an expressive gesture with her white hands, and her rings sparkled in the electric light. "I'll not dispute it in the circumstances."

"You went there with Harry Goldenburg, your husband, in connection with a scheme of blackmail he had conceived. You were to get certain letters from him for Mr. Grell if you could?"

She bowed. "You are correct, as usual."

"Mr. Grell left the room for some reason, and during his absence you had an altercation with Goldenburg."

One slender hand resting on the table opened and clenched. She contemplated her finger-nails absently. "Oh, no," she said blandly. "We were always on the most amicable terms."

Foyle leaned over the table, his face set and stern, and gripped her tightly by the wrist. "Do you realise," he demanded, and his voice was fierce, almost theatrical in its intensity, "that you left your finger-prints on the hilt of the dagger with which you killed that man—indisputable evidence that will convict you?"

She shuddered away from him, but his hand-grip bruised the flesh of her wrist as he held her more tightly. He had timed his denunciation well. The strain she had put on herself to meet the situation snapped with the sudden shock. For a brief second she lost her head. She struggled wildly to release herself. His blue eyes, alight with apparent passion, blazed into hers as though he could read her soul.

"I never left finger-prints," she exclaimed wildly. "I wore gloves.... Oh, my God!"

The superintendent's hand opened. The storm of passion on his face died down. The woman, now with a full realisation of what her panic had done, was staring at him in an ecstasy of terror. Green was writing furiously.

It was Foyle who broke the stillness that followed. "That will do, I think," he said in an ordinary tone of voice, as though resuming a dropped conversation. "Have you got that down, Green? Mrs. Goldenburg,"—he gave her her real name,—"you will be charged with the wilful murder of your husband. It is my duty to warn you that anything you say may be taken down in writing and used as evidence against you."

A hysterical laugh came from the woman's lips. She flung her hands above her head and went down in a heap, while shriek after shriek of wild, uncanny laughter echoed in the room.