Can anyone say what is the relationship or history between Sherlock Holmes and Irene Adler in the 2009 movie Sherlock Holmes. In the movie when they are shown together first time, it seems there is a back story.
The beginning of "A Scandal in Bohemia" describes the high regard in which Holmes held Adler:
To Sherlock Holmes she is always the woman. I have seldom heard him mention her under any other name. In his eyes she eclipses and predominates the whole of her sex. It was not that he felt any emotion akin to love for Irene Adler. All emotions, and that one particularly, were abhorrent to his cold, precise but admirably balanced mind. He was, I take it, the most perfect reasoning and observing machine that the world has seen, but as a lover he would have placed himself in a false position. He never spoke of the softer passions, save with a gibe and a sneer. They were admirable things for the observer--excellent for drawing the veil from men's motives and actions. But for the trained reasoner to admit such intrusions into his own delicate and finely adjusted temperament was to introduce a distracting factor which might throw a doubt upon all his mental results. Grit in a sensitive instrument, or a crack in one of his own high-power lenses, would not be more disturbing than a strong emotion in a nature such as his. And yet there was but one woman to him, and that woman was the late Irene Adler, of dubious and questionable memory.
Note also that:
She is portrayed by Rachel McAdams in the 2009 film Sherlock Holmes in which it is assumed - contrary to Conan Doyle's statement in the original story - that she and Sherlock Holmes did become lovers.