Before Saturday Night Live, before SCTV, there was a scrappy Toronto production of Godspell that somehow assembled comedy’s future royalty in one place.

Martin Short, Eugene Levy, Andrea Martin, Gilda Radner, Dave Thomas, Victor Garber as a hippie Jesus, and Paul Shaffer as musical director. The 1972 show was supposed to run a few weeks. It went for over a year and a half.

While the show was still running, Martin and Levy joined the original Second City Television cast. Garber left to star in the Godspell movie. A few years later, Lorne Michaels was building SNL and cast the first person he remembered from that Toronto production, Radner. The rest is history.

Nick Davis’ documentary You Had to Be There captures the whole unlikely story through interviews with the surviving cast, plus Stephen Schwartz, Dan Aykroyd, Mike Myers, and Lin-Manuel Miranda. Executive produced by Judd Apatow, the film makes the case that this one musical was the petri dish for the comedy revolution that followed.

The doc opens September 18 at Film Forum in New York. For indie filmmakers, it’s a reminder that lightning-in-a-bottle moments happen when the right people collide at the right time.