The Krogers' 'flash transmission' radio equipment, 1960, on display during a preview for the MI5: Official Secrets exhibition at the National Archives in London, Tuesday, April 1, 2025. (Jonathan Brady/PA via AP) LONDON — A desiccated 110-year-old lemon that played a key role in espionage history is one of the star attractions of a London exhibition drawn from the files of MI5, Britain’s domestic intelligence agency. Compact spy cameras, microdots in a talcum powder tin and a briefcase abandoned by fleeing Soviet spy Guy Burgess are also part of the show at Britain’s National Archives, which charts the history of...