All I can remember of the plot is that there was a guy and he had been dating the same girl basically his whole life. A new girl comes to town and somehow they end up together. I believe they were in high school or just graduating from high school. Then at some point it is discovered that the new girl has a secret twin and the secret twin tries to kill someone, I can’t remember who. The secret twin always wore gloves on her hands because there was something wrong with them, I believe they were burned but I’m not positive.

Again I know it isn’t much to go on. For some reason the movie Swim Fan always triggers me to try to find this book.