In the corner of the first-class carriage farthest away from the platform, the Princess Petrovska sat with her hands on her lap and a rug round her knees, glancing idly from under her long eyelashes at the people thronging the Euston departure platform. Her eyes rested incuriously now and again upon a couple of men who stood in conversation by a pile of luggage some distance away, but within eyeshot of the compartment.

She had some vague recollection of having seen one of the men before, and though she remained apparently languidly interested in the business of the platform, she was racking her brains to think who he was or where she had seen him. It was recently, she was certain. Suddenly she leaned forward, and her smooth brow contracted in a frown. Yes—she was nearly certain. He had an overcoat and a silk hat on now, but when she last saw him he had been a bare-headed, frock-coated clerk in the advertisement office of the Daily Wire. The frown disappeared and she dropped back. But behind the placid face an alert brain was working. Had the man followed her, or was it a mere coincidence? Was he a detective? With an effort of will she stilled the apprehension in her breast. Her confidence reasserted itself. Even if he were a detective, what had she to fear? She had merely delivered a cipher advertisement over the counter. It was unlikely that it would be read by others than the person for whom it was intended. Even if it were, there was nothing in it to incriminate her.

Her lips parted in a contemptuous smile.

"I don't believe he is a detective at all," she murmured.

All doubts on the subject, however, were set at rest as the express began to glide out of the station. As though taken unawares by its departure, the man hastily shook hands with his friend and sprinted for the train, swinging himself into the woman's compartment with a gasp of relief.

"Phew," he said. "A narrow shave that," and then, as if realising the sex of his companion, "I—I beg your pardon. I hope the carriage is not reserved. If so, I will change."

She smiled winningly at him.

"No, don't disturb yourself, I beg. It would be a pity after all the trouble you have taken—to catch the train."

Detective-Inspector Blake was not by any means dull. His immobile features gave no sign that he was half inclined to believe the woman was gibing him. "Now, what the devil does she mean by that?" he said, under his breath. He bowed in acknowledgment of her courtesy, and drawing a paper from his pocket unfolded it.

"And how is the charming Mr. Foyle?" said the Princess, speaking with a soft drawl. "I do hope he is still well."

This time Blake was taken unawares. He dropped the paper as though it were red-hot, and the woman laughed. A moment later he was ashamed of himself. She had trapped him into a tacit admission that he was a detective. A surprised denial of acquaintance with Mr. Foyle might have ended in an apology on her part for a mistake. Well, it was too late now.

"So you are a colleague of Mr. Foyle's?" she went on, and though her voice was soft there was a trace of mockery in it. "He is charmingly considerate to send you to look after me. I was desolated to think that I should have to take such a long journey by myself."

"The pleasure is mine," said Blake, falling in quickly with the atmosphere she had set. Nevertheless, he was not quite easy. He recalled the troubles that had beset Waverley, and half regretted that he had not brought his companion on the train with him.

"Smoke, if you like," she said, with a gracious wave of her hand. "I know you are dying to do so. Then we can talk. Do you know, I have long wished to have a talk with a real detective. Your work must be so fascinating."

He took a cigarette case slowly from his pocket, and dangled it in his hand. He had never before seen the Princess, but he was certain of her identity.

"Indeed," he said grimly. "I thought you had met Mr. Foyle. In fact, I believe that he afforded you some opportunity of seeing a portion of the workings of our police system. Do you smoke? May I offer you a cigarette?"

She selected one daintily.

"Thank you. But that was different. I don't think it quite nice of you to refer to it. It was all a mistake. Mr. Foyle will tell you so, if you ask him. Do detectives often make mistakes?"

Her air of refreshing innocence tickled Blake. He laughed.

"Sometimes," he admitted. "I made a mistake just now in coming on this train alone."

She laughed musically in pure amusement.

"I believe the man is afraid of me," she said, addressing the ceiling. Then more directly, "Why, what harm could a poor creature like myself do to a great stalwart man like you? I should have thought you'd greater sense."

"Common sense is my strong point," he parried.

"And therefore you are afraid," she laughed. "Come—Mr.—Mr.——"

"Smith—John Smith."

"Mr. John Smith, then. It's a good English name. I shan't do you any harm. But if you like to lose sight of me when we reach Liverpool——"

"Well?"

"It would be worth £50 to you."

He shook his head. "I am afraid, Princess, you have a very poor opinion of the London police. Besides, I told you just now that common sense was my strong point."

She shrugged her shoulders for answer. The train droned on. They had lunch together and chatted on like old friends. It was when they had returned to their own compartment, and the train was nearing Liverpool, that Blake found his cigarettes had run short. The Princess produced a daintily-jewelled enamelled case.

"Won't you try one of mine?" she asked. "That is, if you care for Egyptian."

He took one. What harm would there be in a cigarette? Yet, in half an hour's time, when the train slowed into Lime Street Station, the Princess descended to the platform alone. In his corner of the compartment Blake slumbered stertorously.