Ferguson sat up with a cry of joy.

“Prove that, Mr. Holmes, and I am your debtor forever.”

“I will do so, but in doing so I must wound you deeply in another direction.”

“I care nothing so long as you clear my wife. Everything on earth is insignificant compared to that.”

“Let me tell you, then, the train of reasoning which passed through my mind in Baker Street. The idea of a vampire was to me absurd. Such things do not happen in criminal practice in England. And yet your observation was precise. You had seen the lady rise from beside the child’s cot with the blood upon her lips.”

“I did.”

“Did it not occur to you that a bleeding wound may be sucked for some other purpose than to draw the blood from it? Was there not a queen in English history who sucked such a wound to draw poison from it?”

“Poison!”

“A South American household. My instinct felt the presence of those weapons upon the wall before my eyes ever saw them. It might have been other poison, but that was what occurred to me. When I saw that little empty quiver beside the small birdbow, it was just what I expected to see. If the child were pricked with one of those arrows dipped in curare or some other devilish drug, it would mean death if the venom were were not sucked out.

“And the dog! If one were to use such a poison, would one not try it first in order to see that it had not lost its power? I did not foresee the dog, but at least I understand him and he fitted into my reconstruction.

“Now do you understand? Your wife feared such an attack. She saw it made and saved the child’s life, and yet she shrank from telling you all the truth, for she knew how you loved the boy and feared lest it break your heart.”

“Jacky!”

“I watched him as you fondled the child just now. His face was clearly reflected in the glass of the window where the shutter formed a background. I saw such jealousy, such cruel hatred, as I have seldom seen in a human face.”

“My Jacky!”

“You have to face it, Mr. Ferguson. It is the more painful because it is a distorted love, a maniacal exaggerated love for you, and possibly for his dead mother, which has prompted his action. His very soul is consumed with hatred for this splendid child, whose health and beauty are a contrast to his own weakness.”

“Good God! It is incredible!”

“Have I spoken the truth, madame?”

The lady was sobbing, with her face buried in the pillows. Now she turned to her husband.

“How could I tell you, Bob? I felt the blow it would be to you. It was better that I should wait and that it should come from some other lips than mine. When this gentleman, who seems to have powers of magic, wrote that he knew all, I was glad.”

“I think a year at sea would be my prescription for Master Jacky,” said Holmes, rising from his chair. “Only one thing is still clouded, madame. We can quite understand your attacks upon Master Jacky. There is a limit to a mother’s patience. But how did you dare to leave the child these last two days?”

"The house in the Square Lamartine is occupied by Prasville's men."

"Don't worry, Sebastiani. I shall get in. If they don't open the door, there's always the window. And, if the window won't open, I shall arrange with one of Prasville's men. It's a question of money, that's all. And, thank goodness, I shan't be short of that, henceforth! Good-night, Daubrecq."

He went out, accompanied by Sebastiani, and the heavy door closed after them.

Lupin at once effected his retreat, in accordance with a plan which he had worked out during this scene.

The plan was sunple enough: to scramble, by means of his rope, to the bottom of the cliff, take his friends with him, jump into the motor-car and attack d'Albufex and Sebastiani on the deserted road that leads to Aumale Station. There could be no doubt about the issue of the contest. With d'Albufex and Sebastiani prisoners; it would be an easy matter to make one of them speak. D'Albufex had shown him how to set about it; and Clarisse Mergy would be inflexible where it was a question of saving her son.

He took the rope with which he had provided himself and groped about to find a jagged piece of rock round which to pass it, so as to leave two equal lengths hanging, by which he could let himself down. But, when he found what he wanted, instead of acting swiftly - for the business was urgent - he stood motionless, thinking. His scheme failed to satisfy him at the last moment.

"It's absurd, what I'm proposing," he said to himself. "Absurd and illogical. How can I tell that d'Albufex and Sebastiani will not escape me? How can I even tell that, once they are in my power, they will speak? No, I shall stay. There are better things to try... much better things. It's not those two I must be at, but Daubrecq. He's done for; he has not a kick left in him. If he has told the marquis his secret, there is no reason why he shouldn't tell it to Clarisse and me, when we employ the same methods. That's settled! We'll kidnap the Daubrecq bird." And he continued, "Besides, what do I risk? If the scheme miscarries, Clarisse and I will rush off to Paris and, together with Prasville, organize a careful watch in the Square Lamartine to prevent d'Albufex from benefiting by Daubrecq's revelations. The great thing is for Prasville to be warned of the danger. He shall be."

The church-clock in a neighbouring village struck twelve. That gave Lupin six or seven hours to put his new plan into execution. He set to work forthwith.

When moving away from the embrasure which had the window at the bottom of it, he had come upon a clump of small shrubs in one of the hollows of the cliff. He cut away a dozen of these, with his knife, and whittled them all down to the same size. Then he cut off two equal lengths from his rope. These were the uprights of the ladder. He fastened the twelve little sticks between the uprights and thus contrived a rope-ladder about six yards long.

When he returned to this post, there was only one of the three sons beside Daubrecq's bed in the torture-chamber. He was smoking his pipe by the lamp. Daubrecq was asleep.