Blake Lively plays Nancy, a medical student taking time off from her studies and plans to go to a secluded beach in Mexico with a pal for some surfing. Let down by her friend she heads alone hoping for a period of self reflection as this was the beach her now deceased mother once visited when she was young.
While she is surfing alone she is attacked by a large shark. Injured, bleeding she is stranded on a rock. She looks for help but no one is about, her medical skills are used to patch herself up the best she can and she realises that she is only safe on the rock as it is low tide. As the tide rises, she needs to get to safety, but the shark is circling round. Nancy needs to somehow outwit the shark.
This is really a low budget B movie. The CGI is ordinary and the story is preposterous. Nancy is in a remote location but she gets excellent wifi and a mobile phone signal.
The shark is of course demented, hell bent in gobbling up Nancy when their are other food sources about (maybe he saw her performance in Savages!)