What story does Enfield tell when he and Utterson pass the door?

The door reminds Enfield of a recent occurrence he witnessed. A strange, repellent man trampled down a little girl. The passengers got so angry with him that they demanded compensation from him, on behalf of the girl. He disappeared in the building to which the door led, only to be back a few minutes later with a 100-pound check. The check was legitimate, but signed by another man, Mr. Jekyll - an honorable and well-respected man whose lawyer Enfield is. This story brings about the two most important names - Mr. Jekyll and Mr. Hyde. The reader won't find out that they are actually one and the same person until the very end of the novel.