On the rebound after a devastating break-up, Lisa (Mandy Moore) is ready for adventure while on vacation in Mexico with her sister Kate (Claire Holt). Still, she’s apprehensive when two handsome, fun-loving locals (Yani Gellman and Santiago Segura) suggest the girls join them for a shark-diving excursion on a boat skippered by Captain Taylor (Matthew Modine). Lowered 16 feet into the Pacific Ocean in a rickety cage, Lisa and Kate catch a once-in-a-lifetime, close-up look at a group of majestic Great Whites. But Lisa's worst fears materialise when the cage breaks away from the boat and plummets 47 metres–more than 150 feet–down to the seabed. To their horror, the sisters discover they are too deep to radio for help without leaving the cage and making themselves vulnerable to the voracious sharks, and a rapid ascent would lead to the potentially deadly condition known as the bends. With their oxygen supplies rapidly dwindling, the girls do everything in their power to get to safety, even as a series of calamitous events makes it increasingly likely they won’t escape their underwater prison alive. A terrifying tale of survival set in the domain of the ocean's fiercest creatures.