What is the most challenging aspect(s) about writing a psychological thriller like The House of Dark Shadows?

A psychological thriller like The House of Dark Shadows is basically writing about a mind game. Not only does it involve a mind game among the characters, but as the writer you’re also playing a mind game with the readers. As the writer, you’ve got to be very careful and very creative in how you present the story. In The House of Dark Shadows you’ll notice that the story is told complete from one character’s point of view. You’re privy to some of his thoughts and emotions, and the reader can get in his head a little bit. However, the readers don’t get any insight into what the other characters are thinking. Instead, you get one character’s perception of what he thinks they may be thinking or what their emotions are; you get his perspective and his perspective alone. Obviously, if you were able to get inside other characters’ heads in the book, you would be able to figure out what was going on pretty quickly. Because of the set up of all of this, you leave the reader wondering whether their take on the book is right or not. Did this really happen or was it part of the character’s imagination or what? Can you take the explanation at the end at face value or was there more to it? Who was the good guy and who was the bad guy? Was everything really as it seemed or not? I’ve had readers tell me that they weren’t sure how to take the ending of the book, that it could go a couple of ways, and I’ve had readers argue both perspectives and not come to a firm conclusion about it. Thus, that’s the nature of the psychological thriller, in my opinion. Some people don’t like that there isn’t a fully explained and clear conclusion, but I liken it to the twist in Alfred Hitchcock’s works—it leaves you wondering for days after you’ve finished the movie or in my case the book.