Carl Matthews is 45 and his life has become very routine. Every day he travels on the 7.39 train where he sees the same unhappy faces doing the same daily commute into Waterloo. Happily married to Maggie, Carl has become predictable. Sally Thorn has recently moved out of London but still travels in daily as she still works as the manager of a health club. A fight over a seat sees Sally and Carl begin talking and suddenly their daily train journeys become much more interesting.

Carl and Sally have to deal with a dilemma after they start an affair. The repercussions for them both could be life-changing, and they cannot help falling in love.