When the lights went up on Showstopper! at Norwich Playhouse nobody knew what to expect, least of all the cast who were waiting in the wings ready to improvise a musical on whatever the audience suggested.

After a brainstorm of musical styles and locations including the Vatican , Dover Ferry terminal and a theme park an audience vote determined that the setting would be a Catholic theme park for a musical which a quick-witted audience member named Caths. And with that the cast bounded on stage with the opening number, a tight, foot-stomping song with catchy chorus and synchronised dance moves on a topic no one could have predicted a moment earlier.

The story quickly unfolded: Everything is holy, blessed and fun at Kansas 's top religious theme park under the auspices of Cardinal Funtime but things take a dark turn when disciple Nigel Littletown takes over and casts the attraction into purgatory. Cue showstopping numbers in the style of Les Miserables and The Rocky Horror Show, a diversion to the biggest ball of yarn in Kansas , random dolphin songs and an intervention from Jerry Springer as God.

The cast and backing band drew on an encyclopaedic musical knowledge and improvisational skills that allowed them to instantly respond to anything that happened on stage or the audience suggested. In one scene the audience nominated a baptismal fountain as a location and three performers instantly created one with scarves and a feather duster. The cast were unfazed when prompted to sing in the style of Gershwin, switch to opera or belt out a rap. They launched into slick songs which would have been impressive even if they had been composed in a week.

The band were equally dynamic, playing by intuition in whatever mood or genre the ever changing show dictated. There were occasional stumbles and scenes which hit a dead end but the cast were quick to adjust and keep the momentum going.

Within a couple of hours joy and godliness was restored to the holy tourist attraction with a cracking finale that had everyone clapping along.

If Caths sounds like a good show you're out of luck, it will never be performed again. But you can be sure the next Showstopper! production will be just as brilliant, spontaneous and unpredictable.