The Shallows (2016)

When her mother dies of cancer, med student Nancy Adams takes a break from her studies to travel the world.  One of Nancy's key objectives is to locate and surf at an isolated beach that her mother visited in the early stages of being pregnant with Nancy.

At first, the beach seems to be everything Nancy hoped it to be, but when she follows a pod of dolphins out into deeper water, things go awry.  There's an injured whale here, and - perhaps attracted by the injured animal - there's also a great white shark lurking beneath the waves.

Luck allows Nancy to survive the shark's first attack, but she's now trapped hundreds of metres from the safety of the shore, and the great white clearly intends to finish the job.  The shark has all the physical advantages in this situation, of course, so Nancy will have to rely on her wits to survive ...

The first half hour of The Shallows is excellent, with some lovely underwater photography and a growing sense of tension and menace.  Things remain quite strong through the middle as well, once the shark makes it attack.  Sure, it seems very unlikely that a great white would bother spending hours stalking a single woman when there's an injured whale right there, but if you're willing to overlook that - and the film does ultimately offer a figleaf justification for the beast's obsession with eating our heroine - then it's got lots of decent set pieces.

In the last 30 minutes alas, the scenario does start to collapse under the growing weight of its own implausibility.  There were a couple of moments where I laughed out loud at developments: something that very much breaks the tension and I am sure was not intended.

If movies-that-make-you-jittery are your thing, then this is certainly worth seeing for the first hour, at the very least.  For the rest, well, just don't think about it too much.  Though it did occur to me afterward that if you treat this film as a sequel to Deep Blue Sea, with this killer shark being an escapee from that movie, then the whole thing makes a lot more sense.  For certain definitions of sense, anyway!