What action causes Mr. Enfield to notice Hyde? Why does Mr. Enfield conceal the name on the check? Given the story Enfield tells, why is chapter one titled "The Story of the Door"?

One night, at three in the morning, Mr. Enfield was walking through town when he saw a disfigured man whom he described as "a Juggernaut," powering through the street maliciously trample an eight-year old girl who was out to fetch a doctor. After apprehending the man, Enfield, the doctor, and the family of the girl decided that, instead of sending for the police, they would blackmail the man to give one hundred pounds to the girl's family. I think Enfield might have wanted to not disclose Dr. Jekyll's involvement.Under a great "weight of consideration," Utterson asks if the man used a key to get into the door, hence the title. Enfield confirms this and the two men vow to never speak of the incident again.