The novel begins with Mr Utterson taking his weekly walk with his friend, Mr Enfield. As they walk they pass through an alley and Utterson comments on a strange, derelict door that they pass. Enfield tells the story of how he saw a young girl being trampled by a strange man.
Enfield pursued the man and demanded he return and make the situation right. The man offers to pay compensation to the girl and goes in the door to return with some cash and a cheque.
Utterson is very interested in this and asks whether the man used a key to open the door, which he did. We learn that the door is the back entrance to Dr Jekyll's house and that the man is Mr Hyde.
Utterson becomes obsessed with Mr Hyde and wants to meet him. He examines Jekyll's will which he has in his safe and discovers that Jekyll has left everything to Mr Hyde. He asks around about Mr Hyde and begins watching the door at all hours.
Finally, he meets Mr Hyde and is shocked by the sense of evil coming from him. Utterson seeks to warn Jekyll but is told by his butler, Poole, that Jekyll is away and that he has been instructed by Jekyll to let Hyde come and go as he pleases. Utterson is worried that Hyde may be blackmailing Jekyll or seeking to kill him to benefit from the will.