The cheapo horror thriller Saw (2004) cleaned up at the box office with its grim tale of two men who wake to find themselves shackled at opposite ends of a grimy, subterranean toilet, captives of a mysterious serial killer. This encore ups the ante with eight strangers who've been locked in a decrepit house, gassed with a slow-acting poison, and left to tear each other apart. The original provided some genuinely creepy moments despite an increasingly absurd story line; the equally silly sequel defuses much of its tension by moving the villain (Tobin Bell) out of the shadows and into a stale conflict with a rumpled police detective (Donnie Wahlberg). Darren Lynn Bousman directed a script he cowrote with Leigh Whannell, who cooked up the first movie. R, 93 min.