Deep in the bowels of London's Churchill War Rooms, shadowy figures are learning how to defuse bombs, crack codes and rooting out hidden microphones.
But the 300 people, some in their sharpest 1940s outfits, are not real spies but enthusiasts trying their hand at being members of the World War II Special Operations Executive.
The night-time event in early October was completely sold out as Londoners in search of the latest way to fill up an evening enjoy a bit of living history.
The War Rooms were the nerve centre of Britain's war effort, where Prime Minister Winston Churchill directed operations against he Nazis, and were converted into a succesful museum in 1984.
The wannabe secret agents are greeted by staff sporting bright red lipstick, hair curlers, berets and retro outfits, before being taken under the streets housing Britain's government buildings and into the nerve centre of its wartime operations.
Among the guests for the special evening, which features three pretend spy missions, are the vintage 1940s band The Polka Dot Dolls, a female trio who sing period songs.
But before gaining access to the heart of Churchill's bunker -- where official wartime staff worked and where Clementine Churchill and her husband had their separate rooms -- the budding James Bonds are called for a "top-secret briefing".
"Welcome, you are in the most secret place in London," says their host "Major Ashdon Wade", dressed in military uniform and leather gloves and with a neat moustache on his top lip.
"I'm sure your parachute session went very well. And of course, I'm sure your French is fluent so congratulations -- Felicitations! You are nearly done. You have three missions left tonight."
'Dream in morse code'
He reveals their first challenge: to find secret microphones planted in the museum by the enemy.
The apprentice agents are given a small detector that makes a noise when it detects a bug, and advance carefully as they wave the sensor over portraits from the Churchill era, extracts of speeches and propaganda posters that hang from the walls.
All this spy business can be thirsty work, so there's plenty of alcohol on hand to steady the nerves.
"It's so much funnier to visit museum like this, plus there is a bar," says Simon Clarke, one of the guests.
For the second mission, they are given a box with six wires, and each contestant has three minutes to follow 11 instructions for defusing the bomb.
"If you need to unplug the red before the black and the blue before the red, it means the order is blue, red, black,", explains Kimberly Harwood to her companion Jeremy, who is deep in concentration.
After two minutes and 15 seconds, their time is up. A few beat the clock but most recruits receive a note saying "DNC" -- "Did Not Complete".
For the third and final mission, cracking a secret code, participants join "Millicent Fawcett", a blonde in khaki uniform and a cap.
She tells her character's story of being recruited into the SOE, the secret British army charged with using espionage, sabotage and local resistance movements to fight the Nazis in occupied Europe.
In fact, Millicent is a doctorate holder from Leeds University called Kate Vigurs.
"After a while, I started to dream in morse (code)," says Vigurs.
The evening was so successful that the War Rooms now plans to repeat the exercise on Valentine's Day next year.
"We have a collection of love letters sent between Winston Churchill and his wife Clementine," says Nina Dellow, a spokeswoman for the War Rooms -- although it's another question whether the bulldog faced war leader was much of a romantic.