In A Change of Heart, Michel Butor describes the observations, recollections, thoughts, and fears of Leon Delmont during a twenty-two-hour train ride between Paris and Rome. For several years, Leon has traveled regularly in the first-class section in order to attend meetings at the Rome headquarters of Scabelli, the Italian typewriter company whose Paris office he directs. For the last two years, Leon and Cecile Darcella have been having an affair during his frequent trips to Rome. Leon has finally decided to separate from his wife, Henriette, and to live in Paris with Cecile, for whom he has found a position with a Parisian travel agency. Leon is paying his own fare for this trip to Rome and he plans to inform Cecile of his decisions.

During this lengthy and exhausting trip, Leon cannot fall asleep. He passes the time by imagining possible biographies for the other travelers in his compartment. His thoughts about his fellow passengers lead him to reflect on all of his previous trips between Paris and Rome, whether he was alone or accompanied by Henriette or Cecile. Perhaps unintentionally, Leon begins to consider the profound meaning of his relationships with these two women. Specific scenes observed through his train window remind him of significant but apparently now-forgotten conversations and experiences. A Change of Heart illustrates very effectively the influence of involuntary memory on the human thought processes. Leon comes to realize that his past has formed his present attitudes and feelings in ways that he had never even suspected. By the end of A Change of Heart, Leon has convinced himself that in the years to come he will be much happier with Henriette than he would be with Cecile. Shortly before his train reaches Rome, he reverses his earlier decision. Leon will not see Cecile during this visit to Rome; instead, he plans to end his affair and return to his wife and children in Paris.