Girl on a Train, by Paula Hawkins

This book contains pure evil. It's a very effective thriller, captivating, written in an innovative style that suits the subject matter very well.

Rachel is the girl on the train, a young woman who rides to London, passing the same houses every day. On the terrace of one of them, she frequently observes a young couple whose life seems idyllic. That changes.

Furthermore, we learn much more about Rachel, as well as the other principle characters in this book, and we are led expertly down the path of mystery and suspense to its amazing conclusion.