It sounds like it might be something out of a James Bond movie, but Russian authorities say it's very real, indeed.
Russian TV has been showing off what looks like a rock, but is actually a sophisticated piece of spy equipment.
Russian State Television says that four members of the British Secret Service, posing as diplomats, put just such a stone in a Moscow park to electronically collect secrets from their Russian contacts.
The TV footage showed an X-ray of the rock, with a battery and memory board inside.
It's a 21st century version of the kind of dead drops that spies have used for centuries. Hollowed-out stones had been a favorite hiding place for secret messages.
The TV report said the British recruited at least one Russian agent, who was given a small handheld computer. Using the palmtop, the Russian could transmit data into the electronic memory hidden inside the rock. Later, members of the British Embassy in Moscow could pass by the rock and use their handheld computers to upload information from the stone.
The TV report showed surveillance pictures, supposedly taken last fall in Moscow, in which British diplomats passed the rock, and tried to retrieve information from it.
An unnamed agent of the Federal Security Service, the successor to the KGB, said that one Russian citizen had been recruited to spy for Britain and was given the equipment needed to send data to the disguised stone, but that he had been caught and arrested.
The British device would keep the Russian agent from having to meet with his British handlers to pass on information.
And it might have worked, except that the stone seemed to break down. The Russian TV report showed diplomats kicking the rock, and later taking it away for repairs.
The incident is giving the Kremlin a chance to attack two of its favorite targets at once: foreign spies and Russian human rights organizations. That's because one of the alleged spies working at the British Embassy also had responsibility for allocating British grants to Russian non-governmental organizations.
The TV footage showed internal embassy documents authorizing grants to organizations including the Moscow Helsinki Group, a human rights monitoring organization, and the Eurasia Foundation, which undertakes a broad range of activities aimed at strengthening Russian civil society.
Russia is suspicious of groups promoting human rights and democracy. New laws have recently been pushed through limiting their activity.
By now linking nonprofits and spies, the Kremlin is suggesting that some humanitarian organizations are up to no good.
"I wouldn't be surprised to find out this whole story was engineered to provide additional arguments for a more restrictive interpretation of the current legislation," says Andrei Kortunov, vice president of the New Eurasian Foundation.
Kortunov said the message from the Russian government was to be suspicious of NGOs: "Look at these guys. They receive money from foreign spies. They cannot be trusted. And any state would protect itself against such types of behavior."
Another alleged recipient of British money, Lyudmilla Alekseyevna of the Moscow Helsinki Group, said that the documents shown in the Russian documentary were clearly fakes, as her group had not received money from the British Embassy since 2004 and the documents shown were from 2005.
The British Foreign and Commonwealth office issued a short statement. "We are concerned and surprised at these allegations. We reject any allegation of improper conduct in our dealings with Russian NGOs. It is well known that the UK government has financially supported projects implemented by Russian NGOs in the field of human rights and civil society. All our assistance is given openly and aims to support the development of a healthy civil society in Russia."
Their statement, though, does not directly deny the spying charges.
British Prime Minister Tony Blair also had little to say about the incident. "I'm afraid you are going to get the old stock in trade of never commenting on security matters, except when we want to obviously," Blair told a press conference in London.
There has been no word from the British Embassy in Moscow about the location of the four diplomats accused of spying. But with their expulsions likely to follow, there's a definite Cold War chill in the air.
By Beth Knobel