In The Strange Case of Dr. Jekyll and Mr. Hyde, the servants and assistants are aware that the doctor is often reclusive and can be a strange individual, especially when working on his projects. As he became increasingly erratic from his frequent transformations into Mr. Hyde, Jekyll acted more and more reclusive and reserved. Because of this, the servants thought he was either being blackmailed by Mr. Hyde (as evidenced by Hyde using checks signed by Jekyll), falling into ill health, or that some other issue may have arisen that they felt it would be imprudent to intervene upon.
Because of their negligence, Jekyll's transformations progressively became worse and more uncontrollable, leading to several people's deaths as well as Jekyll's eventual descent into full transformation without hope for reversal.
Poole comes to see Mr. Utterson and tells him he that thinks his master, Dr. Jekyll, has suffered from "foul play." He says to Utterson:
"I’ve been afraid for about a week," returned Poole, doggedly disregarding the question, "and I can bear it no more."
Poole and the other servants have not contacted Mr. Utterson because they have been confused about what is going on. They know their master often likes to be left by himself, and they haven't wanted to betray him or overstep their boundaries by going to see a third party about him. Now, however, they are all sufficiently worried and upset that they feel they have no choice but to contact someone.
Rather than try to describe what is happening, Poole urges Mr. Utterson to come and see for himself what is going on. When Mr. Utterson arrives, Poole calls out to his master, who answers in a voice that does not sound like himself. The fear that someone else is impersonating their master has frightened the servants.