The Strange Case of Dr Jekyll and Mr Hyde is a gothic novella by the Scottish author Robert Louis Stevenson first published in 1886. The work is also known as The Strange Case of Dr. Jekyll and Mr. Hyde, Dr. Jekyll and Mr. Hyde, or simply Jekyll & Hyde. It is about a London lawyer named Gabriel John Utterson who investigates strange occurrences between his old friend, Dr Henry Jekyll, and the evil Edward Hyde. The novella's impact is such that it has become a part of the language, with the very phrase "Jekyll and Hyde" entering the vernacular to refer to people with an unpredictably dual nature: usually very good, but sometimes shockingly evil instead.

Gabriel John Utterson and his cousin Richard Enfield reach the door of a large house on their weekly walk. Enfield tells Utterson that months ago he saw a sinister-looking man named Edward Hyde trample a young girl after accidentally bumping into her. Enfield forced Hyde to pay £100 to avoid a scandal. Hyde brought them to this door and provided a cheque signed by a reputable gentleman (later revealed to be Doctor Henry Jekyll, a friend and client of Utterson). Utterson is disturbed because Jekyll recently changed his will to make Hyde the sole beneficiary. Utterson fears that Hyde is blackmailing Jekyll. When Utterson tries to discuss Hyde with Jekyll, Jekyll turns pale and asks that Hyde be left alone.