Short Answer 
Mr. Utterson transitions from an enthusiastic detective focused on uncovering a criminal to a worried and emotionally burdened individual as the narrative progresses. His initial excitement gives way to anxiety and apprehension, illustrating the toll that the unresolved case takes on his character.
Step 1: Initial Enthusiasm
At the beginning of the story, Mr. Utterson displays a strong sense of enthusiasm and commitment towards his work. His primary goal is to uncover the identity of the mysterious criminal causing chaos. This initial excitement is a crucial aspect of his character, showcasing his dedication to justice and his professional integrity.
Step 2: Growing Concern
As the narrative progresses, Mr. Utterson begins to exhibit signs of increased worry and anxiety. He feels the pressure of the unresolved case, which weighs heavily on him. The use of phrases like “under a weight of consideration” illustrates his mounting concerns about the implications of the crime and his failure to uncover the truth.
Step 3: Emotional Burden
Mr. Utterson’s character becomes increasingly burdened by his thoughts and feelings. His reactions display a transition from enthusiasm to deep apprehension, reflecting the emotional toll the investigation is taking on him. Words such as “sombre spirits” highlight his declining morale and growing fears regarding the outcome of his quest for the criminal.