A Wiltshire cathedral city may seem an unlikely venue for the 007-like theories currently circulating. But of course Britain has been here before, which is what takes this incident from the improbable to the possible.
Authorities are working to establish what "unidentified substance" affected two people who were found unconscious on a bench outside a shopping centre in the middle of Salisbury on Sunday afternoon.
One of those people was a 66-year-old former Russian military intelligence officer who was convicted of high treason in a Russian court. His identity means that wider questions about what happened and who might be involved are inevitable.
Sergei Skripal was sentenced to thirteen years in prison in 2006 for his crimes against the Russian state, but was eventually handed over to the US in 2010 as part of a spy swap.
The same year Skripal was convicted and sentenced, London was in the grip of a high-profile case involving the murder of a Russian dissident on British soil.
A prominent critic of Russian President Vladimir Putin, Alexander Litvinenko and his family fled to the UK. In late 2006, he went to meet two Russians - Andrei Lugovoi and Dmitry Kovtun - for tea at a central London hotel. Shortly afterwards, Mr Litvinenko fell seriously ill.
When admitted to hospital his condition initially baffled doctors, but Mr Litvinenko told them he believed he had been poisoned.
While such a suggestion would normally stretch credulity, samples of his blood were sent to Britain’s nuclear research centre at Aldermaston in Berkshire. It was there it was confirmed that he had been poisoned with radioactive polonium-210.
The poison had left a trail across London - from the teapot from which Mr Litvinenko drank to a restaurant in Piccadilly where he later met a friend.
That trail of poison also led back to the hotel rooms of the two men Mr Litvinenko had met for tea. It was also found on the plane which had carried Andrei Lugovoi back to Russia.
The two men quickly became prime suspects in the death, although numerous attempts to extradite them from Russia failed.
The death caused a major long-standing rift between the British and Russian governments, with diplomats expelled on both sides.
In 2016 an inquiry into Mr Litvinenko’s death found that his murder had probably been approved by the Mr Putin, which the Kremlin always denied.
As authorities race to find out what caused the illness of Skripal and his daughter, who was visiting him from Moscow, they have appealed for people not to speculate.
Such a request is surely more in hope than in expectation because given the potent mix of spies and suspicion, speculation is never far behind.
