In need of some adventure after a painful break-up, Lisa (Mandy Moore) joins her sister Kate (Claire Holt) on a vacation in Mexico, where they decide to go on a shark-diving excursion with a couple of locals (Yani Gellman, Santiago Segura). However, when Lisa and Kate are lowered underwater, their cage breaks free from the boat and sinks 47 meters down to the seabed. Surrounded by deadly Great Whites and too deep to radio for help, the sisters must find a way to escape the circling sharks and make it safely back to the surface before their oxygen supply runs out.