The idea is great: an elite class trapped in school, forced to solve exam questions to save classmates shown on TV screens in deadly traps. After a slow first half hour, the film keeps the pressure on, with tight editing and inventive kills. Variety praised its "neat concept" and said it had "enough shocks and gore to keep genre addicts contented".
Lee Beom-soo, best known for comedy, is interestingly cast as the tough teacher Hwang, and he brings real presence. Nam Gyu-ri is fine as the rebellious I-na, though most of the students are hard to tell apart.
The problems are the script and the logic. Characters make baffling choices, the riddles are often either too easy or needlessly obscure, and the camera keeps cutting away at key moments. Some critics found the cruelty more ugly than scary. Koreanfilm.org called it "simultaneously tepid and lackluster" and "gross and offensive".
The killer reveal is less convincing than the build-up, and the epilogue is odd. Still, if you enjoy Saw-style puzzle killings, it is a fast, gory 88 minutes.
