Nancy (Blake Lively) has dropped out of medical school. Taking time out in Mexico, she's hitched a ride to a desolate beach for a day of surfing. Armed only with her backpack full of supplies and her surfboard, Nancy parts company with the local who drove her down to the beach, waxes her up her board and paddles out.
In the water are two fellow surfers. Nancy makes small talk with them and soon all three are catching waves and having a good time. As the day goes on, Nancy paddles into shore for a break. She calls her father and sister, and her father implores her to return home and finish her studies. The call upsets Nancy and she decides to head back out into the surf for a few more waves. At the same time, the two locals call it a day, suggesting that Nancy does the same. She says she will - after one more wave. But it's a fateful decision.
Nancy manages to escape the first attacks from the huge shark that inhabits the cove. Then three objects offer Nancy her only chance of survival: a whale carcass, a rocky outcrop jutting out just above the water, and a floating navigation beacon.
Directed by Jaume Collet-Serra, The Shallows is B-movie silliness given a mainstream polish. Realism doesn't make an appearance anywhere in the film, and Nancy's back-story is so minimal it seems like it was written on the back of a coaster in a bar the night before filming began.
The film is very well-shot, with the secluded cove (the beach scenes were shot in Australia) transformed from beautiful at the beginning of the film to eerie and claustrophobic by the end. The filmmakers have employed plenty of tricks, with aerial cameras and Go-Pros used to jazz up the look. The CGI isn't as classy, it gets real silly, real quickly.
But Blake Lively's performance is pretty good. In amongst the heart-racing moments, there are plenty of slower scenes. Like when Nancy is faced with the puzzle of being trapped 200 yards from the shoreline, the navigation beacon a 30-second swim away, and the huge shark circling, hungry for more. Here, the film almost gets subtle, there's almost even some tension. But it doesn't last, soon hurtling headlong back into the absurd.