In the heart of the Selva Maya rainforest, it’s a race against time. ​Cave diver Jose Urbina Bravo and his fellow activists are striving to​ stop the construction of Mexico's largest-ever infrastructure project:​ the Maya Train. They embark on a series of expeditions to survey​ its impact on wildlife and the environment, above and​ below ground. Amid an audacious legal challenge to halt​ development, the group continues exploring the region's intricate​ underground cave system, desperate to document what will be lost.​