On her way into London on the train each morning, Rachel catches a glimpse of a happy couple that she calls Jess and Jason. She thinks they much live a perfect life until one day she sees Jess kissing another man. Jess goes missing soon after.
The story is told from three sides: Rachel, Jess (actually her name is Megan), and Anna (Rachel's ex-husband's new wife who lives on the same street as Jess/Megan).
This book consumed me for an entire day. It's kinda like Gone Girl, but I liked it much, much better.