What story does Enfield tell when he and Utterson pass the door? What does hearing the story cause Utterson to do?

Mr. Enfield tells Mr. Utterson about being on the streets late one evening and seeing a strange man trample a little girl. The strange man just kept going, but Mr. Enfield caught up with him and brought him back to where a crowd of the girl's family and a doctor had gathered. The crowd was angry and the girl's family demanded payment from the strange man of 100 pounds. The man finally agreed. He took them to his house, using a key to enter the door and came out with 10 pounds in gold and a check for the rest.  In the morning, Mr. Enfield and the crowd demanded that he go with them to cash the check. Mr. Enfield noticed a strange address on the check, somewhere on a square, and noted that the check was probably a forgery. He was surprised when the check was genuine.

Mr. Enfield told Mr. Utterson the man's name was Hyde and that he had used a key to get in. Then, Mr. Utterson went home and looked over Dr. Jekyll's will, for he had recognized the name Hyde as his beneficiary. Mr. Utterson had always thought the will odd because Dr. Jekyll left all his possessions to Mr. Hyde in the event of his death or disappearance for a period of three months. Now, in Mr. Utterson was even more suspicious of the will and Mr. Hyde. Here begins Mr. Utterson's investigation into Mr. Hyde/Dr. Jekyll even though at this point he does not know they are one and the same. After reading over the will, he goes to see Dr. Lanyon, who also knows Dr. Jekyll.