The idea of performing an improvised musical is not a new one, and is always likely to enthrall a late-night audience who can never quite comprehend how skillfully their new ideas are weaved into perfect theatrical symmetry by such a talented cast and musicians. Yet Showstopper! has the edge on any I've had the pleasure of seeing in Edinburgh before, for the extra layers it adds - more ideas from the audience; a 'producer' who allows the other performers time and direction to ensure that a storyline is developed and resolved; and the array of props on show that are at times used to hilarious comedy effect.Best of all, however, is the performance of Ruth Bratt, who in this particular rendition plays Lucy, enslaved wife of a pharoah who eventually rises up to assume previously unimagined female supremacy over Ancient Egypt. This musical, which weaves influences from flamenco dancing; High School Musical and the phrase 'Sands of Time' - to mention but three - into its seamless production, is so expertly executed because of the high calibre of talent it has on show, and a format that works so expertly because it has expert on-the-spot scriptwriters at its heart.The group interacts in a way that ensures that the main thread of the story, which sees two Pharoahs fall in quick succession, is carried out to its glorious conclusion (albeit with plenty of bloodshed along the way), and only the harshest of critics would note one or two subplots (and indeed audience submissions) that get lost along the way. The magic of the performance is particularly brought to life by the piano who ably abets the group who are quick to pen their next quip, while the audience are kept engaged and enraptured to the end.While this is undoubtedly a superb use of theatre which draws in audiences night after night and is a must-see, there is a fear that repeatedly seeing the new performances will undo some of the magic as the format is gradually unravelled - so I would hesitate at suggesting seeing the show night after night. But as a one-off, it's superb, a very special Fringe show.