In a horror movie, to go on a camping trip is to march toward a certain and grisly death, usually at the hands of an escaped killer or fanged monster. Seth (Paulo Costanzo) and Polly (Jill Wagner), the foolhardy campers of the terrifically taut Splinter, encounter both. Initially, they’re carjacked and kidnapped by a convict (Shea Whigham) and his drug-addled girlfriend (Rachel Kerbs), but it isn’t long before all four band together to fend off blood-oozing human mutants. One or more of the four may even turn mutant themselves, thanks to the prick of sharp, quill-like splinters whose origins can’t possibly be of this earth. In an impressive debut, English director Toby Wilkins and screenwriters Ian Shorr and Kai Barry don’t fuss over otherworldly explanations, but instead focus on exploring all the ways four people can be hunted down and turned to pulp while hiding inside a gas-station food mart. Buoyed by solid ensemble work, some yuckily effective special effects, and a script that subverts genre convention by having its characters do smart things instead of stupid ones (mostly), Splinter earns our respect while delivering 82 minutes of lean, mean fun.