After extensive rehearsal, the band recorded the basic track in one take, with all four members playing together at the same time. Greg Lake
(later the guitarist for Emerson, Lake & Palmer) was on bass and added the vocals, and Robert Fripp played guitar. These two grew up together and had the same guitar teacher, so by the time they formed King Crimson they were very much in sync. Ian McDonald played saxophone on the track, and Michael Giles was on drums.
Lake and McDonald came up with the distinctive riff for the song, although all four players are credited for composing the music.