Fox has ordered a second script for The Passage, its high-profile drama pilot from Liz Heldens, Matt Reeves, Scott Free and 20th Century Fox TV.

Because of the scope of the project, an adaptation of Justin Cronin’s fantasy book trilogy, which requires longer lead time, the pilot’s production was shifted to summer. It is one of two Fox drama pilots picked up this pilot season that will be shot off-cycle, along with The Beast.

The Passage, which will be helmed by top drama pilot director Marcos Siega, is eyed for a potential midseason launch. A second finished script would help hit the ground running if the pilot is picked up to series.

Written by Heldens, The Passage begins as a character-driven government conspiracy thriller and morphs into a post-apocalyptic saga with vampires. The series spans more than a century and focuses on a young girl named Amy who must save the human race.

Heldens executive produces alongside Reeves and Adam Kassan via 6th & Idaho, Siega, and Ridley Scott and David W. Zucker via Scott Free Productions. Cronin is co-producer.

Cronin’s The Passage trilogy includes the best-selling eponymous first book, published in 2010 by Random House’s Ballantine Books, which was followed by The Twelve in 2012 and The City of Mirrors last year.