Plot: Introduced by Richard Baker BBC2 joins Radio 3 in stereo at the Royal Albert Hall for a live relay of the first half of tonight's Henry Wood Promenade Concert, the opening of the 89th season. Beethoven Mass in c major Ileana Cotrubas (soprano) Kathleen Kuhlmann (mezzo-sop) Robert Tear (tenor) Gwynne Howell (baritone) BBC Singers BBC Symphony Chorus conductor BRIAN WRIGHT London Philharmonic Choir conductor RICHARD COOKE BBC Symphony Orchestra leader BELA DEKANY conductor Sir John Pritchard