The novel is set in a typically foggy London. A young Scotland Yard lieutenant is charged to investigate the mysterious disappearance of corpses from London morgues. The only "explanation" is an abstruse statistical theory that correlates the body-snatching with local cancer rates. The detective, however, since the very beginning suspects the same statistician being the perpetrator. Reality, however, proves less mundane and certainly less comprehensible than he had hoped.
In The Investigation the classic procedural police mystery is turned into a metaphysical puzzle, in which Kafkaesque themes, although updated, are not missing. As in almost all Lem's production, philosophical and epistemological questions are presented under the simple surface of the plot: what is the role of scientific inquiry? What does the existence of competing explanations mean for that goal? The novel also introduces a theme that will later be present in Lem's works: that observations are formed by the properties of the observer's mind, rather than by any properties of the observed.