Story The Sussex Vampire edition endding

"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?"
"I had told Mrs. Mason. She knew."
"Exactly. So I imagined."
Ferguson was standing by the bed, choking, his hands outstretched and quivering.
"This, I fancy, is the time for our exit, Watson," said Holmes in a whisper. "If you will take one elbow of the too faithful Dolores, I will take the other. There, now," he added as he closed the door behind him, "I think we may leave them to settle the rest among themselves."
I have only one further note of this case. It is the letter which Holmes wrote in final answer to that with which the narrative begins. It ran thus:

BAKER STREET,
Nov. 21st.

Re Vampires

SIR:
Referring to your letter of the 19th, I beg to state that I have looked into the inquiry of your client, Mr. Robert Ferguson, of Ferguson and Muirhead, tea brokers, of Mincing Lane, and that the matter has been brought to a satisfactory conclusion. With thanks for your recommendation,
I am, sir,
Faithfully yours,
SHERLOCK HOLMES