Richard Enfield thought that something had gone wrong with Dr. Jekyll. When and why did he think so?

In Chapter One, 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. Amenable, the mysterious man disappeared behind the strange door that Utterson and Enfield had encountered. He returned with ten pounds in gold and a check signed by a very respectable third party, Dr. Henry Jekyll. Fearing the check was a forgery, the doctor, Enfield, and the family forced the man to stay in their company until the banks opened and the check could be cashed. When the banks opened, Enfield cashed the check, and was surprised to find it valid. Enfield could only imagine that the mysterious man had possession of the check as a result of blackmail.