When Kilsip undertook to educate Naball in the business of a detective, he gave him an epigrammatical piece of advice: "Cultivate curiosity." This golden rule Naball constantly followed, and found it of infinite service to him in his difficult profession. He was always on the lookout for queer cases, and when he discovered one that piqued his curiosity, he never rested until he found out all about it. The Red Indian follows the trail of his enemy by noting the most trivial signs, which to others with a less highly cultivated instinct would appear worthless. And Naball was a social Red Indian, following up the trail of a mystery by a constant attention to surrounding events. A casual observation, a fleeting expression, a scrap of paper--these were the sign-posts which led him to a satisfactory conclusion, and he never neglected any opportunity of exercising his faculties. By this constant practice he sharpened his senses in a wonderful degree, and cultivated to the highest extent the unerring instinct which he possessed in discovering crimes.

Consequently, when he found there was no legal authority to be given him in unravelling the mystery of the diamond robbery, he determined to investigate it on his own account, in order to satisfy his curiosity. To a casual spectator, it appeared to be a mere vulgar burglary, in which the thieves had got off with their plunder, and until his interview with Caprice the detective had supposed it to be so. But when he went over in his own mind the peculiar circumstances of that interview, he saw there was a complicated criminal case to be investigated, so he set himself to work to unravel the mystery, and gratify his inquiring mind.

In the first place, he drew up a statement of the case pure and simple, and then, deducing different theories from the circumstances, he tried to get a point from whence to start. He placed his ideas in the form of questions and answers, as follows:--

Q. Was Villiers outside on the verandah when Caprice mentioned where her diamonds were kept?

A. To all appearances he was.

Q. Had he any inducement to steal the diamonds?

A. Undoubtedly. He was poor, and wanted money, proved by his calling on Caprice and asking for some. He said he would be revenged because she did not give him more than a sovereign, and there would be no sweeter revenge than to steal her diamonds, as it would punish her, and benefit himself.

Q. Did he know the room where the diamonds were kept?

A. Yes. Caprice said her bedroom, and as Villiers had been several times to the house before, he knew where it was.

Q. Did Caprice know Villiers had stolen her jewels?

A. Extremely probably, hence her refusal to prosecute, as he was the husband of Madame Midas, whom she had treated so basely. The refusal to prosecute Villiers might be, in Caprice's opinion, an act of expiation.

When he had got thus far, Naball paused. After all, this was pure theory. He had not a single well authenticated fact to go on, but all the circumstances of the case seemed to point to Villiers, so he determined to go on the trail of Villiers, and find out what he was doing.

Mr. Villiers had of late been under the espionage of the police, owing to some shady transactions with which he was connected, so Naball knew exactly where to find him, and, putting on an overcoat, he sallied forth in the direction of the slums in Little Bourke Street, with the intention of calling on a Chinaman named Ah Goon, who kept an opium den in that unsavoury locality.

To his drinking habits Villiers now added that of being a confirmed opium smoker, and was on terms of intimacy with Ah Goon, in whose den he was accustomed to pass his evenings. Naball therefore intended to watch for Villiers, and find out, if possible, when, owing to drink and opium combined, he was not master of himself, what he had done on the night of the robbery after leaving Caprice.

He soon entered Little Bourke Street, and plunged into the labyrinth of slums, which he knew thoroughly. It was a clear, starry night, but the cool, fresh air was tainted in this locality by the foul miasma which pervaded the neighbourhood, and even the detective, accustomed as he was to the place, felt disgusted with the sickly odours that permeated the atmosphere.

Ah Goon's house was in a narrow right-of-way off one of the larger alleys, and there was a faint candle burning in the window to attract customers. Pausing at the door a moment, Naball listened to hear if there was any European within. The monotonous chant of a Chinese beggar could be heard coming down the alley, and every now and then the screams of two women fighting, while occasionally a number of noisy larrikins would come tramping heavily along, forming a strong contrast to the silent, soft-footed Orientals.

Pushing open the door, Naball entered the den, a small, low-ceilinged room, which was filled with a dull, smoky atmosphere. At the end was a gaudy-looking shrine, all yellow, red, and green, with tinsel flowers, and long red bills with fantastic Chinese letters on them in long rows. Candles were burning in front of this, and cast a feeble light around--on a pile of bamboo canes and baskets heaped up against the wall; on strange-looking Chinese stools of cane-work; on bizarre ivory carvings set on shelves; and on a low raised platform at the end of the room, whereon the opium-smokers reclined. Above this ground-floor were two or three other broad, shallow shelves, in each of which a Chinaman was lying, sunk deep in an opium slumber; there was also a kerosene lamp on the lower floor, beside which Ah Goon was reclining, and deftly preparing a pipe of opium for a fat, stolid-looking Chinaman, who watched the process with silent apathy.

Ah Goon looked up as the detective entered, and a bland smile spread over his face as he nodded to him, and went on preparing his pipe, while Naball stood watching the queer operation. There was an oil lamp with a clear flame in front of Ah Goon, who was holding a kind of darning-needle. Dipping this into a thick, brown, sticky-looking substance, contained in a small pot, he twirled the needle rapidly, spinning round the glutinous mass like treacle. Then he placed it in the flame of the lamp, and turned it slowly round and round for a short time until it was ready; then, having placed it in the small hole of the opium pipe, which he held ready in his other hand, he gave it to his countryman, who received it with a grunt of satisfaction, and, lying back, took the long stem between his lips and inhaled the smoke with long, steady breaths. When his pipe was done, which was accomplished in three or four whiffs, he devoted himself to preparing another, while Ah Goon arose to hi............