You Once Said Yes is my favourite festival experience of the 2011 Fringe to date. It starts at the Underbelly, where an officious flight attendant named Cecile checks your bag and issues you with a new one containing mysterious items, including a red rose, a box of mints and a sealed envelope only to be opened in the case of an emergency.

Then you’re directed out onto Cowgate and you’re on your own – albeit only briefly. Over the course of the next two hours or so (the Fringe programme seriously underestimates the running time), you become acquainted, and often deeply involved, with more than a dozen people: a lost backpacker, a nervous bank robber, a balloon animal-making clown accosted by hordes of children on the Royal Mile, a single mum on her lunch break, a lawyer pleading a case in court, a homeless drug addict, an investment banker-turned-gardener, a charity shop assistant, a needy blind date, an exam-cramming student, a wheeler-dealer negotiating a property deal in a bingo hall.

From moment to moment, you have no idea what to expect - except that someone somewhere is expecting you, ready to propel you into another mini-adventure. It’s disorientating and exhilarating and, by the end, when all of your disparate experiences come together in a personalised musical climax, it’s frankly mind-blowing.