Complex sentence: Poole is Jekyll's butler who has lived with him for many years, upon noticing the reclusiveness and changes of his master, goes to Utterson with the fear that his master has been murdered and his murderer, Mr Hyde, is residing in the chambers.
Split into simpler sentences: Poole is Jekyll's butler who has lived with him for many years. Upon noticing the reclusiveness and changes of his master, Poole goes to Utterson with the fear that his master has been murdered and his murderer, Mr Hyde, is residing in the chambers.