A French-speaking officer assures me: "You are safe now," as I bemoan being pinned against a bullet-shattered window, quizzed about my political allegiances, and forced into a dark and dirty underground sewage system, all in the search for good food. As he finally guides me beyond a thin red cloth, separating Secret Restaurant from the outside world, he says simply: "Enjoy your meal."
As I step into the fourth-floor, 1940s-Russian-themed eatery, the eyes of 60 smartly dressed people turn to scrutinise me. Unsure who is a fellow customer or a well-rehearsed performer, we know neither in what film set we are meant to be dining nor who we have sitting by our sides. A portrait of Stalin and an appetiser of pickled herring are clues. But, to my surprise, working out the answer is far from most people's minds.
This is the world of Secret Restaurant – a collaboration between the immersive theatre company Secret Cinema – which recreates the worlds of classic films in mystery settings for customers who do not know what they have bought tickets to see – and the Michelin-starred restaurant St John, known for its unapologetically minimalist style.
The idea, says Fabien Riggall, the 36-year-old founder of Secret Cinema, is that an "aspect of mystery" makes any encounter richer.
"The fact is that we're in a state of overload continuously, telling everyone everything – either on Twitter or on Facebook. We have created something here where we don't tell people anything and there is something in that – it works. The experience starts from when a guest books a table: they are taken into the narrative and are sent a newsletter, which tells them where to meet, what to wear and what to bring. From the moment they receive the email to the time they eat, it is a theatrical experience."
In short, it's like Fight Club, with knives and forks. The 3,600 customers who will pass through the doors of Secret Restaurant over its six-week existence will be, like me, given one piece of advice before they dine: "Tell no one."
Meeting at various points around a building, we are brought to the mystery location by an actor, who guides us through a specially built "underworld". Paying £28.50 for a main course, dessert and aperitif, guests eat staples from St John – a "pot roast", but with "Old Spot Pork Loin, Trotter and Agen Prunes", to give it an eastern European twist. Mini Eccles cakes follow, while police of different nationalities raid the restaurant and Russian pianists play along.
St John's head chef, Chris Gillard, 38, who is overseeing the five other chefs, says it is an "act of certifiable madness" to bring his cooking to the pop-up location, but one he does not regret. "There were challenges: for example, the kitchen here has no tap and no drain – we basically had to run a hosepipe into the kitchen and create a pump to get the waste water out," he says. "But once you get past the excitement of what's in front of you, the dinner becomes a social event, you chat with people around you and the meal becomes more than the sum of its parts."
The Russian "restaurant manager", Boris Arkadievitch Polyakoff, confides that he "works on the black market at night". His guests and I are encouraged to guess what world we inhabit before we join the other 400 moviegoers downstairs, to view the film at the centre of the creation. Handwritten notes are slipped into our hands and we are told "credit cards are accepted – as well as food ration cards" at the end of the meal.
Among the guests – and the 20 actors in the room – is a 21-year-old Apple employee, Xander Edwards, from north London, who has splashed out on two tickets as a gift for his girlfriend, Ilayda. Adamant that he is "not a foodie" and stressing that he has to work two jobs to afford such luxury, he says he enjoys "the strangeness" of the occasion and the chance to "break the norm".
A mother of two, Claire Daniel, 61, has guessed the film already when I go over, while Peter Keyle, 51, from Salisbury, part of a corporate group from the pharmaceutical industry, says it is "all about the anticipation". As 22-year-old fraud detection specialist, James Owers, from central London, is invited by a singing Russian to "buy a forfeited passport", he says: "It's almost a shame I have to sit down to watch a film after all this."
But for Mr Riggall, Secret Restaurant, which he estimates cost £100,000 to run, is not just about the big screen. Planning to launch more stand-alone pop-up restaurants, he says: "You could base it on a painting – we could recreate an Edward Hopper somewhere – it would spring up in part of the city, people would go, eat, and enjoy the performance integrated within it. You choose your own level of involvement... but the food always has to be the most important thing."