Overall, this was a good story. It was a different way to go about introducing a murder mystery, making the reader wonder what was real, or imagined. I was able to figure out who the guilty person was very early in the book, but the writing was good, and will keep many people guessing until the second part of the book.
This story reminded me of Rear Window. A person stuck in his apartment with a broken leg, and he spends all his time watching the lives of the people living across the courtyard, through their apartment windows. Then, something bad happens. Same basic setup, but The Girl on the Train has some interesting twists.