More than a tale about the restoration of order, though, the Mueller investigation is also about the limits of what can be known. Consider, for example, what the report says about Paul Manafort, Mr. Trump’s erstwhile campaign chairman. Mr. Manafort, writes Mr. Mueller, shared polling data produced by the campaign with a man known very likely to be connected to Russian military intelligence. The subplot is full of possibility, but it ends up leading nowhere. Mr. Mueller writes that his office “could not reliably determine Manafort’s purpose” in sharing the information, in part because Mr. Manafort and his colleagues used encrypted messaging to communicate with one another.

Or there’s the question of what Mr. Trump knew or didn’t know about his campaign’s communications with individuals linked to the Russian government, and whether he was truthful in his written answers.

In this, the Mueller report fits neatly into a subgenre known as the “metaphysical detective story” — stories that take Sherlock Holmes’s triumphant cracking of the case and turn it upside down, so the detective’s efforts end in the same disorder with which they began. These are mysteries about the impossibility of ever really solving a mystery, or perhaps of knowing anything at all.

The uncertainties that hover around the Mueller report evoke similar themes. How much can be known about what Donald Trump had in mind when he fired James Comey? Was Mr. Trump intent on stopping the Russia investigation, or was his goal to remove an F.B.I. director who irritated him for other reasons? Will the question of what Paul Manafort was up to remain forever unanswered, the information crucial to solving the puzzle lost? And if the full story of the Russia affair remains beyond the reach of explanation, to what extent does this cast doubt on the whole project of restoring order in the first place?

As in the metaphysical detective story, these factual gaps raise broader questions about the detective’s inability to reconstruct the story of the crime. Put crudely, this is the question of what it means that Robert Mueller can’t save the country. It’s how to understand the effect on the stability of American democracy of both the president’s relative impunity at the end of an investigation that strongly implied he may have committed serious crimes and the nation’s inability to come to grips with the fact of interference by a foreign power in an election.

Or to put it another way: Does anything matter?

Mr. Mueller clearly thinks it does. Testifying before the House Intelligence Committee, he became most animated when he spoke about election interference: “I hope this is not the new normal,” he said, “but I fear it is.”

In this way, the Mueller report may turn out to be more of a film noir than anything else. The detective successfully uncovers the plot, only to discover that the society around him is too rotten to do anything about it. For all the missing pieces in this story, the issue is less whether it can be told and more whether anyone cares to listen.