Since Jacob was small, his grandfather had told him about the island, the safe haven where he grew up, alongside with many other children who could do extraordinary things. His grandfather would take out the strange photos and show Jacob one by one, recalling the fond memories of the girl whom they had to hold down to prevent her from floating away, the twins who could lift very heavy things, the girl who could make fire with her hands, the boy with bees in his stomach, and so on and so forth. It was all fascinating to Jacob, but as Jacob got older though, he could see the implausibility of his grandfather's stories. He could see the amateur manipulation of the photos. And he was mad. He was mad because he loved his grandfather so much and he so wanted to believe his stories. Just before he died from a strange attack by some sort of wild animal in the woods behind his house, his grandfather called Jacob and urged him to go to the island and find the "bird" and this mysterious letter. Jacob was torn. He wanted to respect his grandfather's last wish, but on the other hand, he feared he'd get confirmation that everything his grandfather told him was a lie.
Stories about kids with strange powers are pretty common, but it's the setting and the way the author set it up against a historical period that makes this really intriguing. I was definitely not expecting where the author took the book. Love it!
The book is being sold as a teen book, but it feels a bit like an adult book with kids in it. It's thoroughly enjoyable, and I think Fox has already bought the movie rights to this. Go see the creepy photos, and check out the book trailer here.
I just read an Entertainment Weekly review of this book that makes no mention of it being targeted to teens, but it does make the same X-Men connection you did.