Two sisters, Lisa (Mandy Moore) and Kate (Claire Holt), are on vacation on the coast of Mexico. When they were diving in a shark cage to watch sharks, the rope of the cage suddenly broke and the cage fell to the bottom of the sea 47 meters deep. Due to the low oxygen, they only had one hour to escape the cage and return to the surface. At this time, great white sharks were also swimming around them. The seabed 47 meters deep was pitch black, and they could only observe the situation outside the cage with a flashlight. The voices of the staff on the water surface were intermittent, and the rescue team was nowhere to be seen. The two sisters were very scared. Faced with the remaining oxygen, they had to make a choice immediately to have a chance of survival. In order to avoid the sharks and swim out of the water alive, the two sisters and the sharks launched a thrilling life-and-death battle of wits and courage...