Bizarre: a show that makes you the star of your own film noir

BY rights, I should be red with embarrassment. Sitting in a busy coffee shop in Brooklyn, wearing a fedora hat and reading dialogue out loud in an American accent isn't the way I usually spend a Sunday. But then that's the effect Gyda Arber has on people.

The New York-based actor is the brains behind Suspicious Package, a Fringe show that takes interactivity to a whole new level. Armed with an accessory (fedora, feather boa), a video pod (an iPod with visuals) and an introductory pep talk from Arber, you head off into the streets of Edinburgh's Old Town to star in a witty film noir. Initially alone, you quickly bump into the other characters and exchange brief moments of dialogue, before moving on to another location.

Whether you're cast as the hard-nosed Producer, the clever Detective or the glamorous Heiress, according to Arber even the most timid people find their inner performer. "At the beginning some people feel a little uncomfortable," she says. "But then they get the hang of it, and by the end everyone's having a good time and they're so dramatic in the final scene. People really come out of their shell, and I love watching that happen."

Arber herself has been acting since she was three, and is a regular performer at Brooklyn's Brick Theater. But it was in her capacity as an audience member that the idea for Suspicious Package first came to her. "I love going to interactive theatre but I always find it disappointing," says Arber. "Because either one person gets to do something fun and the rest of the group just watches, or you're all herded along as one big group. So I thought it would be good to have a show where everybody played a part and got to do something really fun."

Putting the show together sounds like a logistical nightmare. With six characters to concern herself with, Arber set about planning who meets who, where, when and why. Then, the iPods were loaded with maps, short clips of film, music, voiceovers, lines of dialogue and flashbacks to give each character a context for their actions. As Arber says "it's hard to explain but super fun to do".

It would seem other people think so, too. A sell-out run in Brooklyn was complemented by glowing words from the press. "We had no idea if it would work because nobody had ever done it before," says Arber. "But the show was so successful. We got amazing reviews and the fact that the New York Times even turned up was unbelievable, because they don't come to a lot of things. It was overwhelming."

Taking part in just a small section of the show, what surprises me most is how safe you feel. Despite not knowing what's going to happen next or what you'll be asked to say, you feel incredibly looked after. Throughout the show, Arber watches from a safe distance to ensure nobody strays from the flock, and she has obviously spent months planning every minute detail.

Having decided to bring Suspicious Package to the Fringe, Arber made a reconnaissance trip to Edinburgh to find the best location for her show. Several venues were interested, but Arber needed a tricky combination of atmosphere and safety - crossing the road while reading an iPod being ill-advised. In the end, C too at St Columba's by the Castle proved perfect.

"Some of the other venues were good," says Arber. "But they just didn't have access to those great little alleyways and stairways, places to hide and watch, the way C too does." Figuring out how long it takes to walk down to the Grassmarket, up Victoria Street and back to the venue was a crucial part of the planning, and one of the most impressive things about the project.

"It's all timed," explains Arber. "If one person goes into a shop, four seconds later somebody else comes in and they have a scene together. So I needed to know where the shop was and exactly how long it takes to get from one place to the next. It's all very precise."

A seasoned actress but rookie writer, Arber co-created the script with her mother Wendy Coyle, and is indebted to her for the humour which drives the show along. "The dialogue is great," says Arber. "My mum's a writer and she really helped me with it. There are a lot of very witty lines - and it's great to have the perfect response come up on your screen when you're talking to somebody. Because in real life you often walk away thinking 'if only I'd said that'. So it's very satisfying in that way."

• Suspicious Package is at C too, various times, today until 30 August, as part of the Edinburgh Fringe.