Why Do What They Did?
Heavens, so they HAVE the ransom money, and they could have just returned the child and be done with it? But, instead, they have shown themselves to the police so they can, what, get MORE money out of the parents for a seance?
I think that Kim Stanley's character is a Lady Macbeth type. Controlling Richard Attenborough so absolutely that he does these things out of cowardice and to appease her. Doubling down on their plot is close to insanity. And so, I think it shows that Kim Stanley's character is clinically unwell. She is sociopathic and obsessive after losing her own child.