The Back to the Future franchise turned 30 this year, and fans are no less obsessive about debating plot theories and fawning over Deloreans than they were when the first installment of the trilogy hit theaters on July 3, 1985.

Now, a new documentary will tell the story behind the movies, with participation from director and co-writer Robert Zemeckis, writer Bob Gale, producer Steven Spielberg, and the film’s original cast.

Back in Time, which hits theaters on Oct. 21—the same day Michael J. Fox arrived in the future in the trilogy’s second installment—recounts the inspiration for the story, the decision to use the Delorean, and the impact the series has had in the decades since its release.

“It really is for me inarguably the greatest time travel movie ever put on film,” says Spielberg in the trailer. Huey Lewis, the musician behind the original movie’s theme, “Back in Time,” that shares a name with the documentary, is also featured. “They picked the right song,” says Lewis.

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Write to Eliza Berman at eliza.berman@time.com.