This is my 5th book in the "Strangers in a Train". I loved it!
We meet Amy who left Seattle and Jeff to pursue a work opportunity. Jeff was upset with how this thing all played out. But after a while he realized how much he misses her and how much he is willing to do to bring her back home to him. He figures he'll take the train she usually takes to work and make her listen to him while on the train - she has no-where to go on the train.. Amy doesn't want to return back home with Jeff. their relationship had its problems and she doesn't think that coming to talk to her on the train will make any difference. In her eyes HIS work always came first - before her - so the opportunity of this new job was what she needed (as an excuse) to leave him.
So we are left with Amy and Jeff on the same train day after day - Him trying to convince her it's going to be different and her trying not to yield to her attraction and love for him when she is trying to make the right decision for herself.