I agree with other viewers that the Louise character is neurotic at best. However, one must consider the era in which the film is set. World War II has ended, and older single women like Louise would like to find Mr. Right and settle down. Enter David, portrayed by Van Heflin, whose ambition is hidden by an exterior that alternates between (1) warm and romantic and (2) cool and aloof. He obviously has strung Louise along for some purpose, and he dumps her when she presses him for a commitment. Like most women of the era, Louise probably has been reared to be emotionally and financially dependent on men, whom she and her contemporaries see as "strong, secure, brilliant and perfect." Whenever a relationship in that era did not work out, society would blame the woman for the failure, never recognizing that men can have flaws, bad motives, and other shortcomings. Hence, there is the neurotic or psychotic condition to which Louise succumbs.<br /><br />It seems obvious to me that David already had staked out a certain business owned by Dean Graham, portrayed by Raymond Massey, and that David was using Louise (Mrs. Graham's nurse) to worm his way into the business and lives of the Graham family and cash in on the goods. Dean, being a kind and well-meaning individual, was blind to David's true ambition to marry Dean's naive and gullible daughter Carol and eventually get control of the business and family fortune. (Of course, once the mission was accomplished, David would use and abandon Carol just as he had used and abandoned Louise). David even brags about his objective to marry Carol and spend the family fortune just before Louise shoots and kills him. However, Louise has her own motives, having internalized the reason for David's abandoning her, and she cannot see the whole picture of David's plot. Inadvertently Louise delivers poetic justice by ending David's ambition and saving the Graham family and fortune.