I really liked it! It had the right amount of horror yet was still tasteful. Example: instead of graphically describing the possible fate of the sisters, it's left almost totally to the readers imagination what would happen if they don't escape their attackers. Sometimes this is even more powerful than a gross out description.
Anyhow, I really like this author and her other story here too, I hope she makes more soon!
Really great start and I hope you keep going. Just one thing: this font against the background wasn't exactly easy on the eyes, so maybe a different font or color scheme would help.