What are Tropes?

Tropes. I've heard about them, but that's about it. So, when I came across an article on tropes for suspense or mystery novels, I was relieved to realize I had used a few. Some suspense tropes are: stalkers, twins, domestic abuse, isolated locals, who in the group did it, erased memory, faking death, must figure out by a deadline, and intelligent psychopath. They have given me a few ideas for book three!