Blake Lively shares the screen with a blood-thirty shark in Jaume Collet-Serra’s trashy, yet highly entertaining thriller. It clocks in at a trim 80-odd minutes, most of which is spent out at sea with Lively’s Nancy as she tries to escape the clutches of a shark who’s already had at her leg, leaving her clung to a rock. The setup is simple, but the scares effective. Collet-Serra utilises the camera well to exemplify the horrible situation, keeping the shark at a minimum effectively to heighten the tension and provide maximum shocks in a few key moments, such as a charged rush to salvage a GoPro camera from an eaten surfer. There’s enough backstory fed out about Nancy – she’s a medical school dropout overcoming her mother’s death – for the audiences to root for her determination to survive, which suddenly takes over about halfway through. Lively is a neat fit; this proving the kind of showcase that should work well for her career while also satisfying audiences appetite for cheap thrills.