Sometimes, someone says something which totally takes your breath away.
Like the Russian embassy, which is evidently fed up with British news organisations referring to Sergei Skripal, who was apparently the victim of a nerve agent attack in Salisbury last weekend which left both him and his 33-year-old daughter critically ill, as a 'Russian spy'.
'He was actually a British spy, working for MI6,' complained the embassy on Twitter.
'Xcuse me? And that, somehow, changes things? 'He wasn't one of ours, he was one of yours -- so that makes it all right.'
In any case, if we want to be totally accurate, Skripal was, or rather he used to be, a double agent -- working for Russian military intelligence while also providing secrets to MI6.
Yes, he betrayed his country. That's what double agents do. Which is why in 2004, he was arrested, convicted of high treason and sentenced to 13 years in prison. In 2010, he was pardoned and released as part of a spy swap for 10 Russian agents who had been arrested in the US.
So Mr, or rather Colonel, Skripal ended up, for reasons unknown, in Salisbury, living a quiet, unobtrusive life, presumably in the belief that the Spies' Code of Honour (is there such a thing?) meant he was safe.
There are some things that we know about Sergei Skripal; there are other things we may learn in the coming days and weeks; and there are some things we will never know. Such is the world known to those who inhabit it as 'the wilderness of mirrors'. (The phrase comes originally from the T.S. Eliot poem Gerontion.)
What we know is that someone tried to kill Skripal. What we may eventually learn, if he and his daughter live to tell the tale, is where, when and how they did it. What we are most unikely to learn for sure is who did it, or why.
We may have our suspicions. I certainly do. But will those suspicions ever be confirmed, by real, hard evidence, of the kind that stands up in court? I think not, or at least not any time soon.
Perhaps Moscow's intelligence chiefs wanted to prove that they have long memories and a long reach. Or perhaps -- more likely in my view -- someone close to the Kremlin with access to nerve agents believed that Skripal was cooperating with private investigation agencies looking into industrial-scale money-laundering and fraud. Billions of rubles of dirty Russian money flow through London every year -- and there are some very powerful, very wealthy people who are anxious to keep their wealth safely squirrelled away.
It's now more than 12 years since another former Russian intelligence agent who also worked for MI6, Alexander Litvinenko, was poisoned and died in London. It is five years since the anti-Putin billionaire Boris Beresovsky was found hanged at his home in Berkshire. Suicide? Who knows?
What they had in common was that they had both turned against Moscow. And according to the news website Buzzfeed News, which conducted a two-year investigation into allegations that Russia has been behind up to 14 murders on British soil, Litvinenko and Beresovsky were just two of Moscow's victims over the past 15 years.
We discovered after the death of Litvinenko that Britain's spy agencies are none too keen on delving publicly into the truth behind all these mysterious deaths. Much better, they feel, to leave them to sort out their own mess well out of the public gaze. After all, what's to be gained if we all can rubber-neck as they wash their dirty linen?
They need to be reminded that we are their paymasters. We pay them to protect us, and when they screw up, we have a right to know. Litvinenko and Skripal risked their lives to provide information to MI6 -- we'll never know exactly what they handed over, and it's probably best that we don't -- but if British spooks can't protect their own agents, we have a right both to ask questions, and to expect answers.
Moscow's State media have been mocking British suspicions that the Kremlin -- or people very close to the Kremlin -- were behind the attack on Skripal. One Russian TV report was accompanied by that notorious archive footage of Boris Johnson swinging helplessly from a zip wire, waving a miniature Union flag.
The message couldn't have been clearer: you expect this clown to protect his own agents? If Britain is regarded as an impotent laughing stock in Moscow, we need to know that.
A brave Wiltshire police officer, Detective Sergeant Nick Bailey, was one of many first responders who put themselves at great risk when they went to the aid of Sergei and Yulia Skripal last Sunday. They, their families, and the rest of us, deserve a full, no-holds-barred investigation into who was behind the attack.