Call it whatever you want—jailhouse rock, incarcerated funk, prison soul. But any way you slice it, Edge of Daybreak’s Eyes of Love is a singular achievement in music history. Recorded live in prison by incarcerated musicians during a strict five-hour window, this 1979 record is an improbable soul music sensation—worlds apart from records such as Johnny Cash’s At Folsom Prison, which was not actually recorded by inmates. “It was years before I even knew it was a prison record—I had no idea about its history,” says Jon Kirby, a music executive, in Alix Lambert’s short documentary about the band.