Sisters Lisa (Mandy Moore) and Kate (Claire Holt) become trapped at the bottom of the ocean when a shark diving expedition led by Captain Taylor (Matthew Modine) goes horribly wrong. When the cable attaching the cage plummets 47 metres to the seabed, the sisters must figure out a way to get back to safety battling injuries, lack of oxygen, and worst of all, bloodthirsty, great white sharks.