This, André Delvaux's second feature film, is an adaptation of the Flemish novelist Johan Daisne's Le Train de l'inertie (De trein der traagheid) (1950): his first feature was also an adaptation from a Daisne novel – L’Homme au crâne rasé (De man die zijn haar kort liet knippen) (1948).
In her article 'Between Surrealism and Magic Realism: The Early Feature Films of André Delvaux' in Yale French Studies No. 109: 'Surrealism and Its Others' (2006), Georgiana M. M. Colvile writes 'Un soir, un train [...] grew out of the opening pages of Nerval's Aurélia and deals with love, death, creativity, and language.' In her conclusion she states 'in Delvaux's early fiction films, surrealism and magic realism dance a pas de deux, with the danse macabre as a negative mirror, traversed by an Orphean quest for love', and says that Delvaux's early films are more in the spirit of Magritte, Paul Delvaux and Gracq than Breton or Bunuel.
Mathias (Yves Montand) is a univeristy teacher of Linquistics at a Flemish university similar to the one in Louvain where there were strikes and demonstrations between 1967 and 1968. He lives with Anne (Anouk Aimée), a French woman ill at ease surrounded by a culture she has no knowledge of. However she assists in the Renaissance play Elckerlijc, which Mathias is producing, and in which the personification of Death is a prominent presence.
Having just had an argument with Anne, he is surprised to find her on the train he takes to give a talk in another town, although the presence of other passengers inhibit the possibility of any communication. (Communication, anyway, is rare and/or non-existent in Delvaux's universe.) On the train Anne asks Mathias for his copy of Le Monde (which of course is French for both 'the world' and 'people' although she doesn't look at it, and the final shot of her alive is of her looking out of the train window in the corridor, although she will never join the outside: when Mathias awakes he sees the newspaper Le Monde in her empty seat, it is as if she has left the world and its people behind her.
Then things go weird. Mathias tries to find Anne but Hernhutter (Hector Camerlynck) can't help him, and when the train stops for no apparent reason Mathias, Herhutter and Val (François Beukelaers) meet at the side of the trainline and the train moves off without them. Herhutter used to teach Mathias, and maybe Mathias taught Val, but as it is we have three people of different ages – perhaps all the same person – in a hostile no-man's-land in the middle of they know not where. Who lit a fire isn't known, but anyway they keep it going and Val roasts potatoes there.
It gets weirder. The trio arrive at a nearby village, no one speaks their language, they go for a meal and are served something they didn't order, Val dances the strangest dance with a female server who could be another personififaction of death, then others join in, the atmosphere is hostile, and then Mathias is transported as if by magic to a train wreck, where he finds Anne dead (although, oddly, apparently as beautiful as before).