In retrospect, it makes sense that backing Bassey would prove formative: So much of Led Zeppelin was about power, poise and drama (or melodrama, if you think of the first album's overwrought "Babe I'm Going to Leave You").

But as any superfan will tell you, "Becoming Led Zeppelin" ends when things are just about to get interesting: a pivot to acoustic folk, a plunge into drug abuse and

DECIDER spoke to director-writer Bernard MacMahon and producer-writer Allison McGourty about this project that was decades in the making.