Angela The book really doesn't give too many details about what the serial killer did to the girls, which in my opinion was unfortunate because the story felt not complete. But, to answer you question, you won't be freaked out by the minimal details it does offer.
Susanne No, this one won't bother you. I'm not into dark/creepy/serial killer themes either and unlike a couple others who replied, I found the balance perfect: the mystery and suspense existed without a lot of blood and gore.
Emma Agree with Maureen and Angela. One of the least scary thrillers I have read. I also wished it was a bit scarier.