 King Crimson's previous album, "Larks' Tongues in Aspic" (on which they had moved decisively away from a more traditional progressive rock sound drawing on American jazz, and towards the influence of European free improvisation), had been recorded by a quintet lineup of the band, including experimental percussionist Jamie Muir.Early in 1973, Muir abruptly left the band – ostensibly due to an onstage injury, but in fact due to an overwhelming spiritual need to retreat from music and spend time in a monastery (something which was not communicated to his bandmates according to the liner notes for the Portsmouth Guildhall show in the Complete Recordings box set).Muir's departure turned out to be permanent.