The story starts off in the streets of London, towards the end of the 19th century.  Mr. Utterson is going for his routine walk with a distant cousin, Mr. Enfield.  While on their walk, the two witness a horrible looking man trample a young girl in the street.  They stop the man, and force him to make amends for this atrocity.  A crowd forms, and they demand that this ugly man pay for his crime.  The hideous man bought off his crime with a check of 100 pounds.  The strange thing about the check was that the name on it was that of notable doctor, and Mr. Enfield wishes to believe that it was blackmail, but it seems legitimate.  Mr. Enfield refuses to tell Utterson the name on the check.

After the encounter in the street, a suspicious Utterson goes home to check on his friend Dr. Jekyll, and the strange change that he made to his will.  The change was that in the case of Dr. Jekyll's death or disappearance, all of his estate was to go to a Mr. Hyde.  He thinks that this Hyde might be blackmailing his friend.  Utterson starts to spend more and more time around the building where he say Hyde, trying to meet him face to face to get a handle on the man.  One time he finally does, and and when he sees Hyde's face he is filled with disgust but cannot figure out why.  He then goes to visit Jekyll, but the butler, Poole tells him that he is not available.  Utterson also realizes that the run down house that Hyde resides in is actually a laboratory connected to Dr. Jekyll's home.  Poole tells Utterson that he and the rest of the staff were told to obey whatever Mr. Hyde tells them to do, as if he was their master.  While throwing a party, Jekyll and Utterson begin talking about his will, and when Utterson mentions Hyde, Jekyll becomes very serious.  He makes Utterson promise that he will carry out what the will says.

A while after the party, a woman witnesses Hyde beat and murder a well known man Sir Danvers Carew.  Utterson leads the police to the house of Hyde, only to find him not at home.  However, they do find a burned checkbook, and expect him to go to the bank, but he never does.  Edward Hyde seemed to disappear from the face of the earth.  Worried, Utterson decides to visit his friend Dr. Jekyll.  Jekyll is not of good health.  He tells Utterson that Hyde is gone for good, and that he will never be found.  He gives a letter to Utterson that is apparently from Hyde, and says that Hyde explains that he is not worthy of Jekyll.  Utterson finds out from Poole that no letters were delivered to the house and becomes suspicious.  He consults an expert on handwriting and finds out that the handwriting on the letter is the same as Jekyll's.

For a while things are going good it seems, Jekyll is back to being his old cheery self, throwing parties and what not.  Then somewhere out of the blue, Poole informs Utterson that Jekyll is not seeing anyone yet again.  Utterson decides to consult his other close friend Dr. Lanyon.  He finds out that Lanyon is not of good health and says himself that he will die in a few days.  He refuses to talk about Jekyll, and vows that Utterson will understand after he dies.  Soon after this meeting Lanyon does pass away, and Utterson receives two letters, one to be read after Lanyon's death, and one after Jekyll's death.

Once again Utterson is on his weekly walk with Mr. Enfield when they go pass the residence of Jekyll.  They see Jekyll in the window and begin to talk to him.  They invite him to join them but he refuses, and then all of a sudden bolts out of sight without explanation.  However, Enfield and Utterson do not discuss this strange occurrence any further on the rest of their walk, they just continue in silence.

The chapter called the last night begins with Poole coming to get Utterson, telling him that something has gone wrong at Jekyll's house, and that he has to come over there right away.  When they get there "Jekyll" says that he is not receiving any visitors, but both Poole and Utterson agree that this "Jekyll does not sound like him, but rather like Mr. Hyde.  They come to the conclusion that Jekyll is in danger and that they must break down the laboratory door to get to the bottom of this.  When they get inside they find the corpse of Hyde on the floor wearing Jekyll's clothing.  They cannot find Jekyll anywhere in the laboratory, but do find a new will that replaces Hyde's name with Utterson's, a note for Utterson from Jekyll, and the final item a sealed packet.

The penultimate chapter explains Lanyon's encounter with Hyde.  Lanyon receives instructions from Jekyll to take some ingredients from his lab and keep them at his house for a man to come to pick up later on.  The man arrives and mixes together a concoction, and before Lanyon drinks the potion and transforms from Edward Hyde to Henry Jekyll.  It was this encounter that would shock Lanyon so much that he would end up dying soon thereafter.

The final chapter is Henry Jekyll's narrative of the story.  Jekylll explains  that he found the need to separtate the evil side of himself from the good side.  He succeeded in doing this by creating a potion that would turn himself into Edward Hyde.  At first it seemed like a good way to get rid of all the evil feelings that were bottled up inside of Jekyll, until Hyde killed Carew, which was taking it too far.  Jekyll then got scared from how uncontrollable Hyde had become, and became especially afraid when he would start turning into Hyde without taking any of the potion.  It was then that he realized the only way to control Hyde and the evils that he would commit to the world was to kill himself, and Hyde along with him.  Jekyll says that by the time Utterson read this letter, Henry Jekyll would be no more.