London, 1944. Dr Montgomery leaves his surgery and walks through the local street market, in search of a toy for the son of some friends. He muses on the way that, back in 1941, battles weren't just being fought against the Nazis...
Winter, 1940-41. Mrs Colter lives with her daughters Ruby and Vera, her daughter-in-law Tillie and their lodger, Tom Mason. A seemingly innocent question about what Tillie is up to quickly escalates into a row.
Later, Tillie walks past a photographer's studio, and sees a picture of her own wedding on the wall. She recalls boarding the train with her husband Jim and the conversation they have when alone together: dreaming about starting a family.
But Jim was reluctant to have children at the onset of war, and a home of their own is still fantasy, though Tillie still loves him. But unknown to her, Ruby has written to Jim telling her about Tillie's relationship with Ted Purvis, a notorious spiv.
Jim applies for leave, but is refused. However, he gives his escort, Corporal Lewis, the slip on the train and runs back to Waterloo, where he bumps into Canadian soldier Mike Duggan, who has been AWOL for six weeks. Duggan shows Jim a hidden exit.
Jim returns to his mother, and asks after Tillie, but is interrupted by a knock at the door. It's the military police, who search the house, finding nothing - though Corporal Lewis, on leaving, tells Mrs Colter that he spotted Jim's belt on the table and advises her to turn him in.
Jim goes to see Ruby and grills her about Ted Purvis - she suggests he look in the Lucky Star. Jim goes there, and gets into a fight with Ted's friend Alf, which results in Jim being knocked unconscious. A military policeman takes Jim to Dr Montgomery. Realising that Jim must be AWOL, Dr Montgomery quickly comes up with a plausible pretext for his lack of papers and, when the two are alone together, gives Jim more information about Ted.
Meanwhile, Ted invites Tillie to dinner, and she hesitantly accepts. This exchange is spotted by Tom Mason, who runs into Jim in the street shortly afterwards. He reluctantly tells Jim where Tillie is, but he arrives just too late. A waiter says that Ted may be at Toni's, a hairdresser's that he has an interest in. On the way, Jim runs into both Mike Duggan and the military police again, and has to hide in a tattoo parlour.
Jim goes to see Toni, and finds an angry, bitter woman, seduced and abandoned by Ted. She suggests trying the Alcazar club. Ted and Tillie are indeed there - he's sweet-talking her, and she's wavering: although she loves Jim, Ted is offering her something tangible, as opposed to Jim's vague and far-off dreams.
Jim enters the Alcazar, and spots Ted and Tillie - but before he can do anything policemen swarm into the club and demand to see everyone's papers. As a soldier, Jim is in a different line from the others, and when he sees them leaving, he runs after them - but gets outside the club only to see them leaving in a taxi.
Jim returns home, dejected. His mother says that Tillie will probably be in the bomb shelter under Waterloo Station. In actual fact, she's been lured into Ted's flat, and although Alf and his girlfriend May are there too, they are quickly told to make themselves scarce.
But Dr Montgomery saw them enter the flat, and he informs Jim - and also offers him advice as to the former boxer Ted's weaknesses as a fighter. Jim arrives to find that Tillie has just slapped Ted, and a fight ensues. Ted initially gets the upper hand, but Jim wins after using Ted's strength against him.
Dr Montgomery tends Ted's wounds, and informs him that he has a medical condition that must mean "wine, women and song must play an increasingly unimportant part in your life". Jim and Tillie are reconciled, and two years later they produce the longed-for child. Dr Montgomery reflects on what he'll think of his parents and all their contemporaries when he grows up.
