Not to be confused with the unauthorised, warts-and-all fan history Sane Inside Insanity: The Phenomenon of Rocky Horror, this is an insider’s account all the way, starring the stage-show-turned-cult-film’s writer and co-star Richard O’Brien. Heck, it’s even directed by O’Brien’s son, Linus O’Brien, a fact you couldn’t really miss given interviewees frequently allude cosily to Richard as “your dad”. Given its provenance, it’s no surprise that no one here says, as they do in the rival documentary, that the 1975 film adaptation is a “shitty fucking movie” – but nevertheless there’s honesty on display, mostly about the slapdash origins of the project and the later mistakes made, including the huge flop when the original stage production tried to transfer from Los Angeles to Broadway.

But even the most diehard Rocky Horror sceptic would have to concede that this account does a more than competent job of explaining what the Rocky cult means to fans. That goes especially for queer viewers who saw their first glimpse of an out-and-proud identity baked right into the plot, and a community that grew up around the film that might accept them for who they were. We get personal, quite moving testimonies from various devotees including drag performer Trixie Mattel about how much it all meant to them, especially those living in areas where coming out was especially challenging. Even more touching are the recollections of one guy who ran away from home and ended up being a hustler in New York City at the height of the Aids epidemic, but feels his survival and HIV negative status may be owed to the fact that he spent every Friday and Saturday night out of circulation in a Greenwich Village cinema doing the Time Warp. Jack Black, meanwhile, remembers how the midnight screenings with their audience participation turned him on to the idea that rock music and theatrics could intersect and create joy.

Of course, fans will be most excited by the big-name interviewees here, which encompass just about every one of the major players who are still alive. These include a now-fragile Tim Curry whose voice is rich as ever if a shade or two huskier; Susan Sarandon, remembering how she had to change digs every two nights when they were filming in Bray in England because the budget was so measly; and a still gamine Nell Campbell who has fond memories of working with the late Meat Loaf on set. Plus, there are many contributions from director Jim Sharman, producer Lou Adler, and costume designer Sue Blane whose wide eyes and giddy manner is so echt-costume designer-y one could die of delight. Through it all we see Richard O’Brien himself, sometimes jamming on a guitar and dropping crisp bon mots, right up to the end when he gets just a little bit weepy thinking about it all. Adorable.

• Strange Journey: The Story of Rocky Horror is in UK and Irish cinemas from 3 October.