The story of
Karl Muller and the fatal lemon

When can a lemon have fatal consequences? If it proves you are, in fact, a wartime spy…
Exhibition
5 April to 28 September 2025
Free
Step inside the hidden world of MI5 and explore the extraordinary stories behind the security of a nation.
For the first time, MI5’s history will go on display to the public in a major new exhibition, made possible through an unprecedented partnership between the Security Service and The National Archives.
Explore the ever-changing world of espionage and security threats through original case files, photographs and papers, alongside the real equipment used by spies and spy-catchers over MI5’s 115-year history.
From counter-espionage and daring double-agents during the world wars, to chilling Cold War confessions and the counter-terrorism of recent times, this historic exhibition will take you behind the scenes of one of Britain’s most iconic institutions.
Keep your eyes peeled – a programme of online and on-site events will be announced soon...
In partnership with MI5.
Take a sneak peek at some of the nearly one hundred items going on show in this exhibition:
Image 1 of 5
Find out how Klaus Fuchs, who worked on the atom bomb, was unmasked as a Soviet spy in 1950. Catalogue reference: KV 2/1258
Image 2 of 5
See the evidence that Josef Jakobs, the last person executed at the Tower of London, was a German spy. Catalogue reference: KV 2/27
Image 3 of 5
Discover how workers at the Testing Laboratory checked post for secret messages during the First World War. Catalogue reference: KV 1/73
Image 4 of 5
Examine MI5's files on William Ewer, who ran a Europe-wide network of Soviet spies in the 1920s. Catalogue reference: KV 2/1016
Image 5 of 5
Learn about the Iranian Embassy siege in 1980, where MI5 deployed listening devices. Catalogue reference: FCO 8/3660
The National Archives is the official archive of the UK government, and England and Wales. We are the guardians of over 1,000 years of iconic national documents.
Everyone is welcome to visit our headquarters in Kew. We put on exhibitions, events and displays and offer reading rooms giving access to our collections there.
The National Archives is located by the River Thames in Kew, 30 minutes from Central London. We offer advice on travelling to us by car, bike, train or bus.
Everyone is welcome to visit MI5: Official Secrets once it opens.
We provide a warm welcome to visitors of all ages, including children and family groups.
We have a café and coffee bar provided by Maids of Honour, a historic local tea room and bakery. It has spacious indoor and outside seating and a soft play area.
On the menu is a variety of high-quality lunchtime meals, sandwiches, snacks, soft drinks, tea and coffee. Vegetarians, vegans and other dietary requirements are all catered to.
The story of
When can a lemon have fatal consequences? If it proves you are, in fact, a wartime spy…
The story of
Security Service files paint a vivid picture of what happened when Anthony Blunt – then employed in the royal household – admitted spying for the Soviet Union.
The story of
Learn how a daring spy played a cunning role in the Allied invasion of Normandy.
Discover codebreaking books, training manuals, secret diaries and more...