Codenamed FORTHWITH, Sergei was betrayed in December 2001. Arrested in 2004, he was convicted of high treason in Russia, but was subsequently included in a prisoner swap in July 2010 and brought to the UK. The journey to the attempt on his life had begun.

The Vienna spy swap was the culmination of a CIA plan to free a specific individual, Gennadi Vasilenko, who had been the Agency’s key mole inside the KGB since March 1979. To acquire the necessary leverage, the FBI swooped on a large network in the United States, ending a surveillance operation, codenamed GHOST STORIES, that lasted ten years. Anxious to avoid further embarrassment over the arrests, Vladimir Putin personally authorized an exchange, unaware of Vasilenko’s true status. It was only after the transaction had been completed, and two further Russian spies were exfiltrated from Moscow, that the Kremlin learned of Vasilenko’s value, and the scale of the deception. For the very first time, a Russian government had been persuaded to release four traitors. The humiliation was complete. As Spy Swap reveals, Putin’s retribution would manifest itself in a quiet Wiltshire market town.