Directed, with more efficiency than novelty, by Matt Bettinelli-Olpin and Tyler Gillett (two-thirds of the collective known as Radio Silence), “Ready or Not” turns the home-invasion thriller inside out. Relentless and thoroughly preposterous, Guy Busick and R. Christopher Murphy ’s script hews to its own batty logic, its frantic pacing peppered with morbid humor. Alex’s coke-fueled sister keeps accidentally killing the help, and a wicked Andie MacDowell, as Grace’s implacably murderous mother-in-law, is clearly having a blast with that ancient bow and arrow.

But it’s Weaving who gives this blunt satire of class warfare a heart. Surrounded by cartoon villains, she’s easy to applaud: There’s no side to Grace, just a fearless decency and school-of-hard-knocks scrappiness that’s never diluted with a nudge or a wink. Her performance — like the tormented way that Adam Brody, playing Alex’s vaguely dissipated brother, delivers his too-few lines — reminds us that extreme wealth is often paid for by the suffering of others. Her deconstructed wedding dress, on the other hand, simply screams that women should think twice before asking for that ring.

Ready or Not

Rated R for ubiquitous splatter and satanic invocations. Running time: 1 hour and 35 minutes.