I'm a confident cyclist but the omens aren't good. Earlier in the day - through serendipity rather than design - I narrowly avoided being knocked off the road by a moron in a Peugeot.

When I arrive at Jubilee Square I am given a bike, video console, earpiece and mic, and I'm invited to cycle off at random.

In Blast Theory's Rider Spoke you are both the star turn and the audience.

The console prompts you to lodge answers to open-ended questions in hiding places around the city.

Through the wonders of wi-fi, your recordings are accessible only to other Rider Spokers who arrive in that precise place.

One of the Blast Theory team tells me, as if going through the motions: "I have to say this - cycle legally. Don't break the law."

"No problemo," I reply as I pedal off through two red lights, light up a fag and crack open a can of Strongbow.

My Nokia N800 makes the kind of reassuring noises you'd expect from sat nav if it had been invented by an eco-warrior. Or a woman.

"You're ok," she cooes, and I feel like I'm being soothed through my first drug experience. I stop on the seafront where I hear my first question: "Describe yourself."

"I'm lazy," I babble, wary of a grubby, but not unattractive, homeless woman who seems drawn by my cider.

"But lazy people invented the wheel and the bicycle because they didn't like walking or carrying things."

I move on and listen to Kirsten's reply to: "Follow someone who catches your eyedescribe them to me."

She sounds like my hippy computer as she describes a woman in a flowery dress "who's very focused on something, who can be proud of herself - that just makes her so special and amazing".

Annoyed that Kirsten is intuiting rather too much from five minutes' stalking, I record an anecdote about following a kind old man offering sweets to children from his car.

Fictional kidnap, recorded for posterity. In the theatre of Rider Spoke, you make your own narrative. I treat myself to another Strongy as the computer dares me to find a place where I feel brave and tell her about it. I head past the Cycling Prohibited sign for a bit of trespassing and "cherry knocking" at Fatboy Slim's seafront mansion.

Emboldened by the prank, I race off and find myself amid a gang of kindred spirits who appear also to have been at the fermented apples.

One youth is spitting expletives and begins punching his mates as his girlfriend pines: "No James - remember the Asbo!" Now this is what I call drama. I give chase as he bangs angrily on doors across the road before I am told: "F*** off or I'll break your computer."

That's my cue and, with apposite timing, my Nokia N800 tells me it's time to head back.

"But before you go," she purrs, sounding more like the Cadbury's Caramel rabbit with every glug of Strongbow, "I want you to make me a promise." Enlivened by the cider, I would have promised her anything.

It turns out she wants me to make a final recording into the mic.

"I won't believe in bad omens any more," I vow. "And I promise never to cycle sober again."

And I mean it. Rider Spoke is the best piece of theatre I've seen this year. And I was the star.