The Chain of Chance
Original title: Katar.
"The fact that I was using a dead man's shirts and luggage didn't faze me in the slightest, and if it was a little hard going at first, then it was only because these things belonged to a stranger, not because their owner was dead."
Written in the style of a detective novel, The Chain of Chance is classic Lem: a combination of action, hard science, and philosophical investigation. An ex-astronaut is hired to look into the death of a wealthy businessman, one of several men to meet a gruesome end after visiting Naples. The authorities suspect a pattern, but neither detectives nor a sophisticated computer enlisted for the investigation can crack the case.
On a trial leading from Naples to Rome to Paris, the ex-astronaut barely escapes numerous seemingly random threats on his life. Having set himself up as a potential victim, he realizes that he may now be the target of a deadly conspiracy - and that the conspiracy is not the work of a criminal mind but a manifestation of the laws of nature. The population has numerically exceeded its critical mass; certain patterns have begun to emerge from the chaotic workings of society. As the ex-astronaut unravels the puzzle, he begins to see that some of those patterns can be fatal.