WASHINGTON — Conspiracy theories always turn out to be nothing more than paranoid fantasy. At their heart lies the notion that while the rest of us blithely go about doing whatever it is we think we’re doing, occult and all-powerful forces are really running the world — starting wars, engineering suspicious plane crashes, surveying the next grassy knoll. Take this stuff too seriously and you find yourself on the corner with the Lyndon LaRouche people, trying to convince passersby that the queen of England is actually a ruthless drug dealer in sensible pumps.But every once in a while, an episode such as the death of Alexander Litvinenko comes along to boost the morale of conspiracy theorists — and remind the rest of us that there does exist a secret world full of characters and plotlines so bizarre and implausible that the bard of betrayal, novelist John le Carre, would be embarrassed to write them.

These clandestine creatures don’t actually run the world, of course. But they seem to think they do.

Litvinenko was the former KGB agent — and bitter critic of Russian President Vladimir Putin, also former KGB — who died in a London hospital November 23 after a brief, devastating and mysterious illness. Doctors suspected poisoning, since that was the most likely reason why a healthy 43-year-old’s hair would fall out and his organs would fail. Finally they identified a most unlikely poison: polonium-210, a radioactive element discovered by Marie Curie in 1898 (for which she later won the Nobel Prize) and named after her native country, Poland. The substance is so deadly if ingested, even in microscopic amounts, that doctors still haven’t done a proper autopsy on Litvinenko for fear of killing themselves in the process.

Polonium isn’t the kind of thing you find at the local drug store. Only a sovereign government is likely to have any lying around, which narrows the field of suspects.

Before he died, Litvinenko blamed his impending demise on Putin, whose enemies tend to meet untimely deaths. Litvinenko was said to be on the verge of obtaining documents — or maybe they were already in his possession, this part is unclear — proving that Putin had staged attacks on Russian civilians and made it look as if Chechen separatists were responsible so that Putin would then be free to wage a brutal war of suppression against the Chechens. In the secret world, this sort of gambit is called a “false flag” operation.

But how had the poison been administered? Polonium isn’t really harmful unless you get the victim to ingest it.

It turns out that on November 1, the day he became ill, Litvinenko met a friend at a sushi bar near Piccadilly Circus. Predictably, this was no ordinary friend. It was an Italian “security consultant” named Mario Scaramella who has described himself as an expert in nuclear materials — according to reports in the British media, which have pursued this story with old-school Fleet Street gusto.

Pretty intriguing, this Scaramella guy, but there’s no apparent reason why he would have wanted to kill Litvinenko, who was apparently an ally. According to the Daily Mail newspaper, Scaramella might have used the sushi bar meeting to pass a document to Litvinenko — there are lots of incriminating documents circulating in the secret world — that contained a hit list of Putin’s critics who have been targeted for death by a group of former Russian spies calling themselves “Dignity and Honour.”

The Daily Mail started to lose me when it also reported that British authorities suspect Litvinenko’s killer might be a “ruthless assassin” — former KGB, of course — named Igor, who is a judo master (like Putin), walks with a limp (unlike Putin), and is thought to have fled to Italy (watch your back, Scaramella).

The whole thing is so over-the-top that you almost expect Dr. Evil from the “Austin Powers” movies to make an appearance. It’s easy to lose sight of the fact that all these cloak-and-dagger characters really exist (although I have my doubts about Igor) and that a man who spoke out against Vladimir Putin’s ongoing consolidation of power really did succumb to a rare, exotic poison. I should point out that British authorities haven’t entirely discarded the possibility that, for some reason, Litvinenko poisoned himself.

Spies, former spies, counterspies, a mysterious character named Scaramella. ... The authorities need to find out quickly just what happened to Litvinenko and banish all this throwback, Cold War-style conspiracy and intrigue to its proper venue: the pages of a thrilling but unconvincing novel.Eugene Robinson’s e-mail address is eugenerobinson(at symbol)washpost.com.