For all its interest in evil, in the dark desires that can bring people to heinous and unforgivable cruelty, and drive them to madness, Macbeth is also a love story, albeit of a twisted kind.  Does Macbeth do what he does out of love for his wife?  Does he give her this because he cannot give her a child, or because a child of theirs has been lost?  The play gives no solid answers to these questions, but their relationship drives the action forward, especially in the series of intense scenes leading up to the first murder and directly following it.  As Lady Macbeth's mind becomes “diseased” with guilt, with sleeplessness, with horror at what her husband is becoming, Macbeth looks on in growing desperation, but must follow the path they have set out together, and step deeper and deeper into blood.