If you are familiar with the improvised hit Showstopper! The Improvised Musical you'll get the idea of CSI: Crime Scene Improvisation almost before the intro music (did I spot the theme from The Sweeney?) has finished. A group of talented ad libbers create a one hour comic crime drama before your very eyes based on your suggestions. It's different every day but judging by the one I saw it should be pretty good fun at any time.