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The title character of Joshua could school the Hogwarts students in a bit of evil Muggle magic. The debut feature of documentarian George Ratliff doesn’t exactly employ the supernatural in its story about a Manhattan boy who’s murderously jealous of his infant sister. After all, any 9-year-old can get his hands on some poison. But being able to psychologically torture your elders, say, or plant Crayola scribblings that any therapist right out of graduate school would recognize as the work of the abused? Now that’s a gift.

The trouble is that in this case, these bwah-ha-ha moves persistently feel like they were carefully spawned from a scripter’s imagination rather than a child’s cunning. Co-written by Ratliff and freshman screenwriter David Gilbert, Joshua is the latest twist on the increasingly tired spooky-precocious-kid thriller subgenre. This bad seed, played by Jacob Kogan, is a meticulously groomed private-school student and piano prodigy. He doesn’t care much for soccer or baseball, which gives him the sense that his racquetball-playing father, Brad (Sam Rockwell), might not be so crazy about him. Joshua relishes the attention he gets from his musically inclined uncle (Dallas Roberts), but it’s not enough to quell his insecurities. And when his mother, Abby (Vera Farmiga), brings home baby Lily, the family’s fawning stresses him out so much that one day he vomits. “Do you ever feel weird about me, your weird son?” Joshua asks his dad later. “You know, you don’t have to love me.”

Don’t worry, Josh—everyone will stop loving you soon enough. The filmmakers make this kid someone you eventually want to strangle. It’s partly Kogan’s irritating stare, which projects blankness just as often as menace. But mostly it’s the character’s, well, weirdness. Joshua doesn’t talk much, but when he does it’s random, wannabe-spooky statements such as “Are we safe, Mommy?” and “Someone died in this apartment.” He’s so stiff and unchildlike that any affection he does show his parents—and especially his little sister—comes off as patronizing. Instead of feeling frightened of Joshua, you’ll probably figure that a good slap could put an end to all the unfortunate things that start happening.

Yet until its absurd end, the film itself is fairly enjoyable. It’s just as much about postpartum depression as it is sibling jealousy, and it’s much more interesting when viewed as a story about a breakdown of a household. As Lily morphs from a gurgling angel to a sack of constant shrieks, Abby slowly begins to lose it. Brad is always working and when he isn’t, he’s of little help, leaving his evangelical mother (Celia Weston) to insist she knows what’s best. Meanwhile, construction on the apartment above the family’s combines with the noise already inside Abby’s head to drive her to popping pills. Farmiga’s fierce performance, with her increasingly mussed hair and vacant, disconnected eyes, is what’s truly unsettling, aided by a subtle, string-heavy score and creepy shots of the long, narrow hallways of the couple’s home. Abby’s eventual madness is deeply rooted and believable. But the Zen kid with one masterfully planned act of evil after another? Be grateful for the film’s scariest moments—which tend to happen whenever Joshua is offscreen.