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 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 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."

“There he is!” said Bennett in a startled whisper. Looking between the branches we saw the tall, erect figure emerge from the hall door and look around him. He stood leaning forward, his hands swinging straight before him, his head turning from side to side. The secretary with a last wave slipped off among the trees, and we saw him presently rejoin his employer, the two entering the house together in what seemed to be animated and even excited conversation.

“I expect the old gentleman has been putting two and two together,” said Holmes as we walked hotel-ward. “He struck me as having a particularly clear and logical brain from the little I saw of him. Explosive, no doubt, but then from his point of view he has something to explode about if detectives are put on his track and he suspects his own household of doing it. I rather fancy that friend Bennett is in for an uncomfortable time.”

Holmes stopped at a post-office and sent off a telegram on our way. The answer reached us in the evening, and he tossed it across to me.

Have visited the Commercial Road and seen Dorak. Suave person, Bohemian, elderly. Keeps large general store.

MERCER.

“Mercer is since your time,” said Holmes. “He is my general utility man who looks up routine business. It was important to know something of the man with whom our professor was so secretly corresponding. His nationality connects up with the Prague visit.”

“Thank goodness that something connects with something,” said I. “At present we seem to be faced by a long series of inexplicable incidents with no bearing upon each other.“For example, what possible connection can there be between an angry wolfhound and a visit to Bohemia, or either of them with a man crawling down a passage at night? As to your dates, that is the biggest mystification of all.”

Holmes smiled and rubbed his hands. We were, I may say, seated in the old sitting-room of the ancient hotel, with a bottle of the famous vintage of which Holmes had spoken on the table between us.

“Well, now, let us take the dates first,” said he, his fingertips together and his manner as if he were addressing a class. “This excellent young man’s diary shows that there was trouble upon July 2d, and from then onward it seems to have been at nine-day intervals, with, so far as I remember, only one exception. Thus the last outbreak upon Friday was on September 3d, which also falls into the series, as did August 26th, which preceded it. The thing is beyond coincidence.”

I was forced to agree.

“Let us, then, form the provisional theory that every nine days the professor takes some strong drug which has a passing but highly poisonous effect. His naturally violent nature is intensified by it. He learned to take this drug while he was in Prague, and is now supplied with it by a Bohemian intermediary in London. This all hangs together, Watson!”

“But the dog, the face at the window, the creeping man in the passage?”