Plot: Tonight's visit to the Royal Albert Hall for the 91st season of Henry Wood Promenade Concerts introduced by Jane Glover features the London Sinfonietta now one of the world's leading chamber ensembles. In a concert of 20th-century music conducted by David Atherton they play Janacek's Rikadla, a new work by Harrison Birtwistle, Secret Theatre, specially commissioned by the London Sinfonietta for the composer's 50th birthday, and the Suite from The Threepenny Opera - Kurt Weill's uncompromising but unique and witty theatre music