FOUR SPANISH MATHEMATICIANS GATHER FOR A WEEKEND ONLY TO REALISE THEIR MYSTERIOUS HOST MAY BE TRYING TO KILL THEM IN THIS FIENDISH THRILLER, WHERE SOLVING A SERIES OF BRAIN-TEASER PUZZLES BECOMES THE UNLIKELY KEY TO SURVIVAL.

Horror fans will discern echoes of the Saw franchise here, but thankfully writer-directors Luis Piedrahita and Rodrigo Sopeña don’t require blood and gore to sustain tension, relying instead on a walls-closing-in device which harks back to Star Wars and was elaborated on in Vincenzo Natali’s micro-budget classic Cube. If you’re already imagining a quartet of eggheads whizzing through advanced calculus as if their lives depended on it, fear not, since the conundrums which flash up on a PDA in the locked room for the foursome to solve before the floor space shrinks yet further are riddles inclusive enough to give the audience a chance of coming up with the answers. That said, if do you work out how to time 9 minutes using sand clocks of 4 and 7 minutes before the characters crack it on screen, best not to shout it out in the auditorium!

Puzzles alone won’t sustain a feature through ninety minutes, so the script’s smart enough to unpeel a few layers off the characters, as claustrophobic tension prompts them to reveal hitherto secret connections between apparent strangers. The cast rises to the occasion too, youthful upstart Santi Millan playing off suave oldie Luis Homar, while nervy inventor Alejo Sauras looks odds-on to crack first, and Elena Ballesteros supplies a touch of glamour. In a world of dumbed-down celluloid, how refreshing to see a film which revels in challenging your intelligence. — Trevor Johnston.