This film almost feels like three separate entities spliced together. The opening is okay, and the middle quite excellent, but it fumbles the ball badly towards the end, replacing invention with run-of-the-mill horror cliches. A group of animal liberationists break into a lab, but one member is caught and sent to jail. A year later, a mysterious email alerts those on the outside to the fact that he is now "assisting" with some human experiments, so they decide to raid the research facility and rescue their ally. Initially, the place looks deserted - then they find an elevator going down, and that's where things start to get really interesting... For it's as if they've fallen through a rabbit-hole, into a world where the rules are different, and anything can happen, as they soon find out.
I can't really say much more: it delivers some interesting twists with nicely conspiratorial angles, and De Selva divulges information at the right pace. However, he doesn't have quite enough to divulge, so ends up running out of plot too early; once that's done, he doesn't have anything left in his bag of tricks. Some later scenes play out like badly thought-out computer game puzzles - "Okay, character A has to distract the monster, while Character B makes his way across the bridge to blow up the fuse-box" - and that's a shame, given the well-crafted tension built up previously. With imaginative deaths, good splatter and a surprisingly good performance from Brown (a.k.a. Scary Spice), this is still a pleasant offering, occasionally reaching the heights of greatness.