British-born, divorcee Kay Marshall had no ambition to become a spy, but in the early 1960s she found herself centre-stage of one of the most important and intriguing Australian espionage cases of the Cold War. For two years, Australia’s intelligence agency, ASIO, filmed covert meetings in Sydney between Kay and Ivan Skripov, a high-ranking KGB officer. Unknown to Skripov, Kay was a double agent working for ASIO, codenamed ‘Sylvia’. The case reached a climax in late December 1962 when Skripov dispatched Sylvia to Adelaide, where she was to rendezvous with an unknown KGB operative and deliver a package containing a sophisticated, miniature message sender that could communicate with Moscow undetected. By the time Sylvia arrived at the rendezvous point, ASIO had it staked out with surveillance officers, undercover Commonwealth Police and a photographic team. ASIO’s aim was to detain the mystery man, interrogate him and crack the spy ring. But the KGB’s man failed to appear. The collapse of the case haunted ASIO for the rest of the Cold War. Were there too many surveillance men on the ground? Was there a mole inside ASIO? And who was the mystery KGB operative? Six decades on, investigative filmmaker Peter Butt accessed dozens of reels of ASIO’s surveillance footage taken during the Skripov case. The footage revealed a remarkable story from beginning to end of a brave female agent at the front line of the Cold War. But in one of the reels taken at Adelaide, Peter noticed something odd playing out within metres of the rendezvous point – something that ASIO had clearly failed to investigate…