The Strange Case of Dr. Jekyll and Mr. Hyde 
Written by Robert Louis Stevenson
Dr. Jekyll and Mr. Hyde 
Written by Samuel Hoffenstein and Percy Heath
Directed by Rouben Mamoulian
The story of Dr. Jekyll and Mr. Hyde is such a part of our culture that attempting to describe the plot at first seems a bit redundant. We all know that the virtuous Dr. Jekyll devises a potion which unleashes his inner evil, the nefarious Mr. Hyde. Since this revelation is the novella's final twist, one may even question the need to read the book at all. But Stevenson's book is well worth reading more for what you don't already know than what you do.
It is initially surprising how little the titular character(s) occur(s) within the text. The protagonist is the lawyer Utterson. It is through his investigations that we are introduced first to the foul character of Hyde, and then to the benevolent Jekyll. The most important events in the book are generally related to the reader through conversations between Utterson, the doctor Lanyon, and/or Jekyll's manservant Poole. The rest appear in letters from sealed envelopes, opened in the last twenty pages or so. In lesser hands all this textual circumambulation would quickly grow tiresome. But Stevenson balances each new discovery with a new twist, allowing the reader to piece together more of the story each go around.
What is also interesting are the characters of Jekyll and Hyde as they appear in the novella. Jekyll is a fifty-year-old man. Some of the impetus to create his potion comes from the need to deal with his younger debauches (whether to negate them or indulge more in them is an issue which could be debated). He is a perfect Victorian gentleman, completely compartmentalizing his unacceptable thoughts and letting them out sporadically in societally designated ways. Hyde is something altogether tougher to describe. There are no specific descriptions of him; "troglodytic" seems to be the best adjective used. He's much shorter than Jekyll, sometimes referred to as a dwarf, and has knotty, harry hands. He is also substantially younger, somewhere in his early twenties. As with Jekyll, we are never given descriptions of Hyde's debauches, though we are given testimony to his murder of Sir Danvers Carew, M. P. (We do not witness the act; we must rely on the account given by a maid who spied the attack from a balcony. )
Perhaps the best metaphor for a modern reading of Strange Case is that of a puzzle. You already know what it's going to look like; the fun comes from the reassembly of the image.
Any fun to be had with the 1931 film adaptation is surely unintentional. Time has not been kind to Frederic March's iconic Hyde. The arch-fiend now comes across like a Batman villain, overacting at every single turn. The film's Jekyll is rather young, so his Hyde (the unleashed id) is less the freed expressions of an old debauch than the world's horniest, geekiest monkey man. March obviously studied monkey behavior; his Hyde sniffs the air and swings about like the best of his primate kin. The special effects are passable. The initial transformation, achieved by filming makeup though a series of successive filters, is very well done (only to be undone by Hyde's hamming); each successive metamorphosis is less welcome because we know it will bog the film down in more ridiculousness.
Great liberties are taken with the text's plot. Utterson is utterly absent. Jekyll takes center stage. He's to be married to Muriel, the daughter of Carew, now a general. But he has a secret longing for a pretty bar girl named Ivy whom he saved on the way back from his fiancé's house. In case we didn't get the two sets of contrasts (Jekyll-Hyde and Muriel-Ivy), Mamoulian has the habit of employing split screens to push the symbolism. Sometimes it works, but it's a tad overused.
Oh, and man shouldn't tremble in God's domain. Admittedly, the hint of a moral does appear in Stevenson, but it's secondary to the mystery. We get no such shelter in the film; at one point Hyde even grips a bible and begs God for help. The final shot of the film, after Hyde has been done away with, is of a boiling kettle overflowing into its fire. You know, like Hell. Where the good Jekyll is going. 'Cause he transgressed the limits of human knowledge. (And he killed a hooker and a general, but it's the knowledge transgression thing that really puts him on the Almighty's shitlist.)
The 1931 Dr. Jekyll and Mr. Hyde is a film classic which I really tried to give the benefit of the doubt. But it's creaky and melodramatic to the point of overkill. And all of its pre-Code excesses (moderate as they may be) are severely diluted by the sermonic tone of the film's last half hour. Give the book a read instead.