A terrible epidemic is rapidly spreading in American hospitals in Afghanistan, in which the infected are literally decomposing alive. The disease is caused by a rare and rapidly mutating bacterium. It is extremely important to immediately stop this infection, otherwise a large-scale pandemic will break out with the highest mortality rate. The medicine can be obtained only in one place on earth - in the Mexican super-cave Cueva de Luz, where at incredible depths a special bacterial substance is contained - “moon milk”. The US government is sending there a small expedition of specialists in various fields. Among them is microbiologist Hallie Leland. She has already been to this cave once and knows the route. Daredevils will have to first go through the twilight zone, then the dark zone. And finally, penetrate into the most dangerous zone - the deep. Even more dangerous because there is a traitor hiding in the same squad as Hallie...