mystery novels

I noticed that, it's kind of annoying. But I suppose with as many books as there are out there, there can't possibly be an original story, know what I mean? I love Mary Higgins Clark (a mystery writer), but I have to admit that a lot of her stories are the same, and are similar to other mystery authors as well. If it's a good story, I guess I don't really mind, but in retrospect, it's hard to remember which are which (if they are all the same).