The Girl on the Train by Paula Hawkins - Kindle Edition

Rachel catches the same commuter train every morning. She knows it will wait at the same signal each time, overlooking a row of back gardens. She's even started to feel like she knows the people who live in one of the houses. 'Jess and Jason', she calls them. Their life - as she sees it - is perfect. If only Rachel could be that happy.

And then she sees something shocking. It's only a minute until the train moves on, but it's enough.

Now everything's changed. Now Rachel has a chance to become a part of the lives she's only watched from afar.

Now they'll see; she's much more than just the girl on the train...