This is the second "Jumper" book by Steven Gould. It takes place a little more than 10 years after the first book.
I had an incredibly hard time reading this, but at the same time I had to keep reading it because I wanted to get past what was happening. I ended up reading it in maybe a day and a half since I wanted to get Davy out of where he was. There were huge chunks that I just cried through because the bad guys were doing such horrible things to him.
Which isn't to say it's a bad book, it's not. I wouldn't have cared what was happening to him if it were a bad book!
I very much hope that there'll be more books with Davy and Millie, I like them a lot and I want to know what happens to them. But I'd really like them to be happy! I realize you need some kind of conflict or there's no plot, but maybe something not quite so extreme next time?