How many ways are there to depict infidelity, on screen or on the page? Or romantic love, for that matter? Sometimes it seems that all possible shades of both have been covered, and repeated ad nauseum. Then there comes something like 'The 7.39', and one realizes the same old story can indeed be told in yet another way, which is both entertaining and insightful.
Two commuters - 'everyman' and 'everywoman' - are attracted to each other; the first part focuses on them and the tension is built up really effectively. The second part takes us through the repercussions of their actions, not in a moralistic way, but in a way that one feels sympathy for ALL the characters.
The resolution is unexpected -- I couldn't predict till the last minute how it was all going to end. To take a theme/plot that has been told a million times before, and then to tell in a way that the viewer holds her breath, eagerly anticipating the next turn in the course of events: that's the art of storytelling at its best. This has been compared to the great film 'Brief Encounter'; both deal with the very human theme of temptation, but I think 'The 7.39' also tells us something about the dilemma of the modern man/woman: is life any less complicated when the rules are relaxed?