Showstopper! The Improvised Musical at The Ambassadors Theatre, London A New Musical Every Night! Showstopper! the Improvised Musical sees an incredibly versatile cast & crew work together to create a brand new musical every night, with a theme, title & musical genre all provided by the theatre audience. Masters of long-form improvisation, Showstoppers’ spontaneous & fully-formed productions have to be seen to be believed. The production returns to the Ambassadors Theatre following a successful run earlier this year, not to mention another fantastic season at the Edinburgh Festival Fringe.