Rachel, title character in The Girl on the Train takes the same commuter train every day. She fantasizes about the lives of the people she sees in houses backing up to the tracks. Lives that are certainly happier than her own miserable state.
It would be spoiling a lot to say much more about Rachel’s misery because Paula Hawkins does such a beautiful job of taking us step by step into her life and heart and mind. Every step reveals a new surprise, like tiptoeing down a hallway and looking into different doorways as we go. Suffice it to say here that Rachel’s not satisfied to stay with her voyeuristic imagination. She sees (imagines?) something she must investigate, and her investigation reveals circumstances about the people she’s seen and their imagined lives that contradict her fantasies.
Oh, and it turns out she shares a past with them.
Oh, and there’s murder involved.
Oh, and, well . . .
You’ll just have to read it yourself. To say any more would be telling. . .