This documentary bears witness to the events that took place more than thirty years before the filming of this movie, on October 17, 1961, in Paris, during the Algerian War. It is a work not only about historical truth but also about memory. Constructed primarily from interviews conducted with those involved in the events, along with archival footage, photographs, and radio broadcasts from the time, our investigation proves that nearly 200 Algerians were killed (drowned, tortured) that night and in the days that followed by the French police. "A Missing Day" seeks to ask two key questions: how could such events have unfolded in the capital of a Western democracy barely thirty years ago? And why have they been silenced ever since?