“After , I think we’d always had the idea of one long piece that could carry a whole album,” says keyboard player Tony Banks, referring to the epic, 23-minute centrepiece of 1972’s album. “You could call a concept album, except that it’s such a dirty word these days.” Along with ’s and , David Bowie’s , Jethro Tull’s and Pink Floyd’s , Genesis’s is one of a handful of releases that defined the concept album genre.

This sprawling, 1974 double album has been an essential touchstone for those who’ve developed the style over the last 30 years: Rush, Styx, Queensrÿche, Iron Maiden, Marillion and (despite their denials) Radiohead. You can find websites that give a line-by-line an analysis of Genesis’s lyrics and more theories and meanings than you can throw a colony of Slippermen at. Not that was greeted that way when it was released in late 1974.

The story of a Puerto Rican New York punk named Rael and his surreal adventures in the underworld, as told by a bunch of English public schoolboys, did not exactly set critical pulses racing. The dense plot, sprawled across a double album, was impenetrable to many reviewers who decided it was pretentious. “It got a pretty mixed response in terms of reviews – and from the fans, initially,” Banks remembers.

“People tend to look back and see it as the culmination of the early era of the band, but it wasn’t seen that way at the time. It was darker than our earlier albums, and being a double album it too.