What is the main conflict in The Cat Who Saw Red by Lilian Jackson Braun?

The Cat Who Saw Red is a story about a newspaper writer who stumbles into a murder mystery that begins when he agrees to help an old girlfriend leave her jealous husband. Jim is unable to find any proof of what has happened to Joy, though he knows that what her husband, Dan, has been telling just doesn't add up in any respect. Jim is able to finally figure out what has happened but not before Dan realizes how close Jim is and attempts to kill Jim as well.