The major theme that can be detected in all of Lawrence's fiction is the power of passion and how it often overpowers the intellect and reason. This is of course expressed primarily in this story through the character of Ferguson, who is described as a man who owes his success to his scientific knowledge. Thus he is amazed when he finds that his body acts almost of its own accord in responding to Mabel. Note how this is described in the following quote:
As he kissed her, his heart strained again in his breast. He never intended to love her. But now it was over. He had crossed over the gulf to her, and all that he had left behind had shrivelled and become void.
The phrase "He never intended to love her" clearly indicates that Ferguson falls in love with Mabel against his own better judgement, and from this point on in the short story he half regrets what he has done but at the same time feels that his feelings towards Mabel are inescapable. Passion and its role in overwhelming our judgement and reason is thus a major theme in this novel, as it is in other works of his.