Aspiring University of Florida swimmer Haley Keller receives a call from her sister Beth who informs her that a Category 5 hurricane is on a collision course with Florida and advises her to get out of the state. Haley is concerned for the safety of her father Dave, as he is not answering his phone. Against the instructions of Florida State Police, Haley navigates around evacuation routes to check in on Dave. She first goes to his condo, where he has been living since he and her mother divorced. Haley finds the family dog Sugar at the condo but not Dave himself and is worried that he has returned to the family home in Coral Lake, which he supposedly sold years ago.
Haley and Sugar navigate the flooded streets and find Dave's truck at the Coral Lake house. There, she descends into the crawl space underneath it, leaving Sugar upstairs and finding her father unconscious and wounded; when she tries to drag him out, her exit is cut off by large and ravenous alligators which Dave believes got into the house via a storm drain open to the crawl space. The gators are too large to fit around the pipes under the house, allowing Haley and Dave a safe area at the far end of the crawl space. But with the hurricane intensifying and the crawl space beginning to flood, Haley attempts to navigate around the alligators before she and her father drown.
While attempting to escape the crawl space and fending off the alligators, Haley drops her phone (which gets crushed), discovers that the secondary exit to the crawl space is blocked, tries to contact a group of looters for help before they get attacked, and is helpless to stop the gators from attacking and mauling two police officers who investigate the house for survivors. Dave manages to kill a gator by splitting its head open with a shovel, but gets trapped. In a last ditch effort to escape, Haley makes her way to the storm drain, where she discovers that the gators have made their nest and laid eggs. Haley successfully kills the other alligator using a gun retrieved from the body of one of the police officers and makes it upstairs, crow-barring the living room floor open and saving Dave from drowning in the basement.
Free of the crawl space, Haley, Dave and Sugar attempt to procure the looters' boat just as the eye of the hurricane moves over the neighborhood and the flood waters break the nearby levees, flooding Coral Lake even more and crashing them back into the house, where they get separated. While Dave and Sugar make their way up the stairs, Haley navigates around the kitchen and uses a discarded police radio to broadcast a distress signal to authorities.
After retrieving a set of road flares and saving Sugar from being attacked, Dave loses an arm to one of the alligators. Haley attempts to flag down a rescue helicopter from an upstairs bedroom but is attacked by another alligator and the alligator attempts to drown her in a death roll. While Dave and Sugar escape to the attic, Haley stabs the alligator in the eye with a flare, and attempts to swim to the roof from the outside of the house, narrowly avoiding being mauled by a fourth gator before it gets swept away. Haley lights a flare and flags down the rescue helicopter as Dave and Sugar watch on.
- Kaya Scodelario as Haley Keller
- Barry Pepper as Dave Keller
- Ross Anderson as Wayne Taylor
- Anson Boon as Stan
- Jose Palma as Pete
- George Somner as Marv
- Ami Metcalf as Lee
- Moryfydd Clark as Beth Keller
- Annamaria Serda as Emma
- Savannah Steyn as Lisa