Robert Louis Stevenson 
The Strange Case of Dr Jekyll and Mr Hyde and Other Tales of Terror 

Everyone has a dark side.
Dr Jekyll has discovered the ultimate drug. A chemical that can turn him into something else. Suddenly, he can unleash his deepest cruelties in the guise of the sinister Hyde. Transforming himself at will, he roams the streets of fog-bound London as his monstrous alter-ego.
It seems he is master of his fate.
It seems he is in complete control.
But soon he will discover that his double life comes at a hideous price…