Dr Jekyll creates a potion whereby he can divide the good and evil parts of his personality and thus free the good side to work for the benefit of mankind without the distraction of his baser instincts. Unfortunately, he undertakes the experiment while the depraved side of his nature is in the ascendancy and turns into the repulsive Mr Hyde, whose very presence "emanates with foulness and decay," and who bears the "signature of Satan" on his face. Hyde eventually commits murder and begins to dominate the tortured Jekyll, inhabiting the Doctor's body more and more - and then Jekyll's supply of the drugs to make his potion and effect the transformation start to run out!
The idea for this horror story came to Stevenson in a nightmare. Part thriller, part mystery the novel's construction was also notable, for the action is described by three of the protagonists.
The terrifying tale was hailed as a literary landmark when it was first published in 1886.