Off you go, with the others, finding and solving clues, bumping into shifty civilians (actors), on a tour of the immediate district, an area that includes lots of pubs, dank cellars, Southwark Cathedral, the South Bank and a forgotten rose garden; there, unattached to the performance, two teenage girls are snogging each other as we scratch our heads and fumble with the evidence.
Tom Salamon’s participatory promenade show - following a blueprint tried out in New York and California - is so much better than en route in Edinburgh, because there is a real propulsion to the mission, and it’s more fun with other people. I’m better at crosswords than codes, and our group of eight nearly fell at the last fence, but there is always a safety-net number to ring.
It was somehow comforting to find Oliver Senton of School of Night and Showstopper in the small cast. But is it theatre? More like a very good hunt-the-thimble charade at a surprise party. Good mental work-out and physical exercise, though: you’re on your toes, and on your feet, for nearly three hours.