Of course, the story is very familiar, so we are not surprised or particularly horrified to discover that Dr. Jekyll and Mr. Hyde are one and the same. But no matter, the point of the story remains: be careful of the choices you make or they may come to permanently define you.
Dr. Jekyll has been experimenting on himself with a serum that transforms him into an alter ego, Mr. Hyde. As Hyde, Jekyll engages in horrifying behavior. As family and friends become bewildered at the relationship between the two, Jekyll finally loses control over his ability to go back and forth between them. Finally, he realizes he will be forever Hyde as a result of his inability to stop using the other personality for his own personal gratification.
I love the last paragraph which clearly spells out Stevenson's intended theme,
About a week has passed, and I am now finishing this statement under the influence of the last of the old powders. This, then, is the last time, short of a miracle that Henry Jekyll can think his own thoughts or see his own face (now sadly altered!) in the glass. Nor must I delay too long to bring my writing to an end; for if my narrative has hitherto escaped destruction it has been by a combination of great prudence and great good luck. Should the throes of change take me in the act of writing it, Hyde will tear it in pieces; but if some time shall have elapsed after I have laid it by, his wonderful selfishness and circumscription to the moment will probably save it once again from the action of his apelike spite. And indeed the doom that is closing on us both has already changed and crushed him. Half an hour from now, when I shall again and forever reinduce that hated personality, I know how I shall sit shuddering and weeping in my chair, or continue, with the most strained and fearstruck ecstasy of listening, to pace up and down this room (my last earthly refuge) and give ear to every sound of menace. Will Hyde die upon the scaffold? or will he find the courage to release himself at the last moment? God knows; I am careless; this is my true hour of death, and what is to follow concerns another than myself. Here, then, as I lay down the pen, and proceed to seal up my confession I bring the life of that unhappy Henry Jekyll to an end.
