Affleck the director knows how to build dread. The first act is genuinely gripping, all ticking clocks and hushed phone calls and the awful calculus of how much your child is worth versus how much your career is worth. The script (which Affleck reportedly had a hand in shaping) keeps the geography simple - a house, a car, a handful of rooms - and lets the performances carry the tension.
Washington is the film's engine. Abigail is the one doing the ugly math, and Washington plays her with a coiled, furious intelligence that makes the character feel dangerous even when she's standing still. Affleck is reliably solid in the lead, though he's smart enough to let his co-star take the wheel whenever the scene needs a jolt. Steven Yeun is an inspired piece of casting as a slippery fixer type, and Gillian Anderson, Adriana Paz, Luis Gerardo Méndez, and Ray Fisher round out a cast that's frankly stacked for a movie this lean.
Where Animals stumbles is in its third act, when it starts reaching for Big Themes - political corruption, class, the rot beneath polite society - and the tight little thriller balloons into something baggier. The dialogue gets speechier. The stakes get louder. A movie that was thrilling because it was contained starts to feel like it's auditioning for a prestige limited series. There's also a nagging sense that the film pulls its punches right when it should go for the throat (a kidnapping thriller that's shy about the kidnapping is a strange beast).
At 106 minutes, it never drags, and Affleck's eye for a good frame - all that glass and California sunlight turned menacing - keeps the thing watchable even when the story wobbles. It's a solid programmer with an A-list cast, the kind of mid-budget adult thriller Hollywood supposedly stopped making. Let's be glad somebody still is.