It was eminently suited to the purpose, being entirely surrounded by unoccupied land. For what ostensible purpose Ferrara has leased it, he could not conjecture, nor did he concern himself with the matter. The purpose for which actually he had leased the place was sufficiently evident to the man who had suffered so much at the hands of this modern sorcerer. To approach closer would have been indiscreet; this he knew; and he was sufficiently diplomatic to resist the temptation to obtain a nearer view of the place. He knew that everything depended upon secrecy. Antony Ferrara must not suspect that his black laboratory was known. Cairn decided to return to Half-Moon Street without delay, fully satisfied with the result of his investigation. He walked rapidly back to where the cab waited, gave the man his father's address, and, in three-quarters of an hour, was back in Half-Moon Street. Dr. Cairn had not yet dismissed the last of his patients; Myra, accompanied by Miss Saunderson, was out shopping; and Robert found himself compelled to possess his soul in patience. He paced restlessly up and down the library, sometimes taking a book at random, scanning its pages with unseeing eyes, and replacing it without having formed the slightest impression of its contents. He tried to smoke; but his pipe was constantly going out, and he had littered the hearth untidily with burnt matches, when Dr. Cairn suddenly opened the library door, and entered. "Well?" he said eagerly. Robert Cairn leapt forward. "I have tracked him, sir!" he cried. "My God! while Myra was at Saunderson's, she was almost next door to the beast! His den is in a field no more than a thousand yards from the garden wall--from Saunderson's orchid-houses!" "He is daring," muttered Dr. Cairn, "but his selection of that site served two purposes. The spot was suitable in many ways; and we were least likely to look for him next-door, as it were. It was a move characteristic of the accomplished criminal." Robert Cairn nodded. "It is the place of which Myra dreamt, sir. I have not the slightest doubt about that. What we have to find out is at what times of the day and night he goes there--" "I doubt," interrupted Dr. Cairn, "if he often visits the place during the day. As you know, he has abandoned his rooms in Piccadilly, but I have no doubt, knowing his sybaritic habits, that he has some other palatial place in town. I have been making inquiries in several directions, especially in--certain directions--" He paused, raising his eyebrows, significantly. "Additions to the Zenana!" inquired Robert. Dr. Cairn nodded his head grimly. "Exactly," he replied. "There is not a scrap of evidence upon which, legally, he could be convicted; but since his return from Egypt, Rob, he has added other victims to the list!" "The fiend!" cried the younger man, "the unnatural fiend!"