Carl Matthews (David Morrissey) is stuck. At the age of 45 his life has become routine. Every morning Carl fights his way onto the 7.39 train where he sees the same unhappy faces doing the same daily commute into Waterloo. Happily married to his best friend from college, Maggie (Olivia Colman), with whom he has two healthy, if sullen, teenage kids, life for Carl has become predictable.Sally Thorn (Sheridan Smith) has recently moved out of London, where she still works as the manager of a health club. But she’s unsure if she likes her new suburban life and is anxious about the prospect of marriage to Ryan (Sean Maguire), an enthusiastic personal trainer. Ryan is desperate to start a family, get married, settle down. Not that there’s much time to worry about these things, not while she’s running to catch the 7.39.Over a fight for a seat one morning Sally and Carl begin talking and suddenly their daily commute becomes a lot more interesting.