Half an hour thereafter, a carriage drew up at the side entrance of the Warburton mansion, and a gentleman leaped out, ran lightly up the steps, opened the door with a latch-key held ready in his hand, and disappeared within. The carriage rolled away the moment its occupant had alighted.

In another moment, a man, who had been lounging on the opposite side of the street, faced about slowly, and sauntered along until he reached the street corner. Turning here he quickened his pace, increasing his speed as he went, until his rapid walk became a swift run just as he turned the second corner.

At ten o’clock of this same morning, the Chief of the detectives is sitting again in his sanctum, his brow knit and frowning, his hands tapping nervously upon the arms of his easy chair, his whole mind absorbed in intensest thought. Usually he meets the problems that come to him with imperturbable calm, and looks them down and through; but to-day the thought that he faces is so disagreeable, so perplexing, so baffling,—and it will not be looked down, nor thought down.

Up to the date of this present perplexity, he has found himself equal to all the emergencies of his profession. Living in a domain of Mysteries, he has been himself King of them all; has held in his hand the clue to each. His men may have worked in the dark, or with only a fragment of light, a glimmer of the truth, to guide them. But he, their Chief, has overlooked their work, seeing beyond their range of vision, and through it, to the end.

Always this had been the case until—yes, he would acknowledge the truth—until this all-demanding Englishman had swooped down upon him with his old, old mystery, and taken from the Agency, for his own eccentric uses, its two best men. Always, until Van Vernet and Richard Stanhope had arrayed themselves as antagonists, in seeking a solution of the same problem.

Following up the train of thought suggested by the re-reading of his diary, the Chief has been suddenly confronted with some unpleasant suspicions and possibilities.

He has pondered everything pertaining to the mystery surrounding Vernet’s improper use of his business letter-heads, and his visit to the Warburton mansion in the guise of Augustus Grip. And he has vainly tried to trace the connection between these manœuvres and some of Stanhope’s inconsistencies.

In the search, he has made a discovery: Alan Warburton, the uncle of the lost child for whom his men have been vainly searching, and Leslie Warburton, the widow of the late Archibald Warburton, have both sailed for Europe. Business connected with the search has been transacted through Mr. Follingsbee; and this voyage across the sea, at so inopportune a time, has been treated by the lawyer with singular reticence, not to say secrecy.

What could have caused these two to make such a journey at such a time? Why did Van Vernet enter their house in disguise? Who were the two that had sailed to Europe by proxy? What was this mystery which, he instinctively felt, had taken root on the night of the fruitless Raid?

“It was young Warburton who had secured Vernet’s services, and afterwards dismissed him in such summary fashion. It was Mr. Follingsbee who had engaged Stanhope, for that self-same night, for a masquerade. If I could question Stanhope,” he muttered. “Oh! I need not wait for that; I’ll interview Follingsbee.”