Just when you thought they'd picked the bones of the shark genre clean, along comes this great white bum-squeaker from B-movie maestro Jaume Collet-Serra (House Of Wax, Orphan, Non-Stop). At a beach so secluded it has no name, lone surfer Nancy (Blake Lively) suddenly finds herself targeted for consumption by a dirty great [white] shark. Stranded a mere 200 yards offshore, Nancy must somehow get back to dry land in one piece - using little more than her wits and her wetsuit. Never has a stone's throw seemed so far away...
Not to be outdone by husband Ryan Reynolds' feat of keeping viewers in suspense for 80 minutes from inside a coffin, Blake Lively here attempts to do likewise from a boulder in the middle of the sea.
She plays Nancy, a Texan wave junkie who, following in the wake of her late, surf-loving mother, makes a pilgrimage to a secret surf spot somewhere in Mexico (though actually filmed in Australia).
How she got there without knowing its name is but one of the mysterious contrivances thrown up by a daftly entertaining aqua-thriller that has more holes in its set-up than a shark-savaged surfboard.
After afternoon's hard surfing, Nancy suddenly finds herself alone in the water with a carnivorous leviathan that wastes no time in taking a nibble at her thigh. Injured, marooned (first on a dead whale, then on a rock), and with no prospect of rescue, she's going to have to save herself.
They say tide waits for no man. But Neptune certainly cuts Nancy a break, as where the waves were previously big enough to capsize a cruise ship, the ocean barely rises above a ripple for the rest of her ordeal.
By 'Neptune', we obviously mean director Collet-Serra who - as the man behind House Of Wax, Orphan, and the Neeson-powered triple-whammy of Unknown, Non-Stop and Run All Night - knows that credibility doesn't have to be an obstacle to thrills and suspense.
Efficiency is maintained by having Nancy's backstory conveyed entirely by smartphone, while a wounded seagull not only offers a bit of light relief (she calls it Steven - arf!) but provides a handy sounding board for her ideas.
The effects won't give James Cameron any sleepless nights. Like Jaws, the shark is scarier the less you see of it, while a batch of flares appear to have been supplied by Wile E Coyote.
But director and star work hard to ensure that nobody is going to leave before Nancy's predicament is resolved. In fact, this is a rare movie in which the leading lady actually lives up to her name.
Unlikely to keep anyone out of the water then, but perfect bait for a Friday night.