Little is what it seems as several Spanish mathematicians receive details of a puzzle on the understanding that quick solving of same will lead to a follow-up invitation to a weekend of problem solving in the country. Successful and intrigued, they turn up at the rendezvous, find enigmatic instructions for their onward travel, receive a mathematical nom de plume, and are plunged into a situation, perhaps partly inspired by the Sherlock Holmes story "The Engineer's Thumb", where their survival depends upon their quickness in puzzle/problem solving.
The movie positions itself in that familiar place where horror and whodunnit come together, but this is quite a glossy package, what with the tricksy opening credits, insistent sub-techo music, creepy soundtrack and slick editing. There is plenty here to keep you on the edge of your seat, even if the ending is a little anti-climactic and one is left with a feeling that beneath the slick outer shell of the picture, once the smoke and mirrors are left behind and the several puzzles are solved, little of substance remains.
An intriguing piece of entertainment, though I can't imagine many people wanting to watch it more than once.