Plot: The 117th season of the Proms gets under way at the Royal Albert Hall with music by Brahms, Liszt, Janácek and a world premiere curtain-raiser by British composer Judith Weir. Nineteen-year-old pianist Benjamin Grosvenor makes his Proms debut as the soloist in Liszt's dramatic 2nd Piano Concerto and there is an international line-up of soloists for a performance of Janácek's extraordinary choral work, the Glagolitic Mass