The Girl on the Train by Paula Hawkins

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. Their life - as she sees it - is perfect. If only Rachel could be that happy. And then she sees something shocking, and in one moment everything changes. Now Rachel has the chance to become 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...

This is a paperback edition with red page edges.