The two boats fastened to the little pier that jutted out from the garden lay rocking in its shadow. Here and there lighted windows showed through the thick mist on the margins of the lake. The Enghien Casino opposite blazed with light, though it was late in the season, the end of September. A few stars appeared through the clouds. A light breeze ruffled the surface of the water.

Arsene Lupin left the summer-house where he was smoking a cigar and, bending forward at the end of the pier:

"Growler?" he asked. "Masher?... Are you there?"

A man rose from each of the boats, and one of them answered:

"Yes, governor."

"Get ready. I hear the car coming with Gilbert and Vaucheray."

He crossed the garden, walked round a house in process of construction, the scaffolding of which loomed overhead, and cautiously opened the door on the Avenue de Ceinture. He was not mistaken: a bright light flashed round the bend and a large, open motor-car drew up, whence sprang two men in great-coats, with the collars turned up, and caps.

It was Gilbert and Vaucheray: Gilbert, a young fellow of twenty or twenty-two, with an attractive cast of features and a supple and sinewy frame; Vaucheray, older, shorter, with grizzled hair and a pale, sickly face.

"Well," asked Lupin, "did you see him, the deputy?"

"Yes, governor," said Gilbert, "we saw him take the 7.40 tram for Paris, as we knew he would."

"Then we are free to to act?"

"Absolutely. The Villa Marie-Therese is ours to do as we please with."

The chauffeur had kept his seat. Lupin gave him his orders:

"Don't wait here. It might attract attention. Be back at half-past nine exactly, in time to load the car unless the whole business falls through."

Why should it fall through?" observed Gilbert.

The motor drove away; and Lupin, taking the road to the lake with his two companions, replied:

"Why? Because I didn't prepare the plan; and, when I don't do a thing myself, I am only half-confident."

"Nonsense, governor! I've been working with you for three years now... I'm beginning to know the ropes!"

"Yes, my lad, you're beginning," said Lupin, "and that's just why I'm afraid of blunders... Here, get in with me... And you, Vaucheray, take the other boat... That's it... And now push off, boys... and make as little noise as you can."

Growler and Masher, the two oarsmen, made straight for the opposite bank, a little to the left of the casino.

They met a boat containing a couple locked in each other's arms, floating at random, and another in which a number of people were singing at the top of their voices. And that was all.

Lupin shifted closer to his companion and said, under his breath:

"Tell me, Gilbert, did you think of this job, or was it Vaucheray's idea?"

"Upon my word, I couldn't tell you: we've both of us been discussing it for weeks."

"The thing is, I don't trust Vaucheray: he's a low ruflian when one gets to know him... I can't make out why I don't get rid of him... "

"Oh, governor!"

"Yes, yes, I mean what I say: he's a dangerous fellow, to say nothing of the fact that he has some rather serious peccadilloes on his conscience."

It is possible that the serum of anthropoid would have been better. I have, as I explained to you, used black-faced langur because a specimen was accessible. Langur is, of course, a crawler and climber, while anthropoid walks erect and is in all ways nearer.

I beg you to take every possible precaution that there be no premature revelation of the process. I have one other client in England, and Dorak is my agent for both.

Weekly reports will oblige.

Yours with high esteem,

H. LOWENSTEIN.

Lowenstein! The name brought back to me the memory of some snippet from a newspaper which spoke of an obscure scientist who was striving in some unknown way for the secret of rejuvenescence and the elixir of life. Lowenstein of Prague! Lowenstein with the wondrous strength-giving serum, tabooed by the profession because he refused to reveal its source. In a few words I said what I remembered. Bennett had taken a manual of zoology from the shelves. “ ‘Langur.’ “ he read. “ ‘the great black-faced monkey of the Himalayan slopes, biggest and most human of climbing monkeys. Many details are added. Well, thanks to you, Mr. Holmes, it is very clear that we have traced the evil to its source.”

“The real source,” said Holmes, “lies, of course, in that untimely love affair which gave our impetuous professor the idea that he could only gain his wish by turning himself into a younger man. When one tries to rise above Nature one is liable to fall below it. The highest type of man may revert to the animal if he leaves the straight road of destiny.” He sat musing for a little with the phial in his hand, looking at the clear liquid within. “When I have written to this man and told him that I hold him criminally responsible for the poisons which he circulates, we will have no more trouble. But it may recur. Others may find a better way. There is danger there — a very real danger to humanity. Consider, Watson, that the material, the sensual, the worldly would all prolong their worthless lives. The spiritual would not avoid the call to something higher. It would be the survival of the least fit. What sort of cesspool may not our poor world become?” Suddenly the dreamer disappeared, and Holmes, the man of action, sprang from his chair. “I think there is nothing more to be said, Mr. Bennett. The various incidents will now fit themselves easily into the general scheme. The dog, of course, was aware of the change far more quickly than you. His smell would insure that. It was the monkey, not the professor, whom Roy attacked, just as it was the monkey who teased Roy. Climbing was a joy to the creature, and it was a mere chance, I take it, that the pastime brought him to the young lady’s window. There is an early train to town, Watson, but I think we shall just have time for a cup of tea at the Chequers before we catch it.”

It is a most singular thing that a problem which was certainly as abstruse and unusual as any which I have faced in my long professional career should have come to me after my retirement, and be brought, as it were, to my very door. It occurred after my withdrawal to my little Sussex home, when I had given myself up entirely to that soothing life of Nature for which I had so often yearned during the long years spent amid the gloom of London. At this period of my life the good Watson had passed almost beyond my ken. An occasional week-end visit was the most that I ever saw of him. Thus I must act as my own chronicler. Ah! had he but been with me, how much he might have made of so wonderful a happening and of my eventual triumph against every difficulty! As it is, however, I must needs tell my tale in my own plain way, showing by my words each step upon the difficult road which lay before me as I searched for the mystery of the Lion’s Mane.