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If it’s hard to consider St. Vincent’s Strange Mercy a misstep—-its ideas are too strong, its resolve too robust—-it’s still easy enough to hear it as a failure to build on the foundations laid down on the first two records by the woman known to the taxman as Annie Clark. Maybe a little bit too easy, in fact, adding as the album does to a slim but vital discography that has already given us the relentless pop and whirr of “Actor Out of Work,” the jarring discordance between the easygoing music and unsettling lyrics of “Laughing With a Mouth Of Blood,” and the eager explosion of synapses in “Now, Now.”

Strange Mercy aims to follow suit, but Clark’s success rate is suddenly off. There are times—-starting with the clattering, buzzing coda to opener “Chloe in the Afternoon”—-where you half-expect her to leap up like a mad scientist from her lab and throw a curtain across the room while screaming, “Don’t look at it! It’s not ready yet!”

Then again, boilerplate St. Vincent can still be delightfully surprising, as is the case with “Cheerleader.” (It deflates retroactively thanks to the subsequent “Surgeon,” which is unfocused and wiggy, serving almost as chillout reprise). “Cruel” could be a dance song, kinda, sorta, maybe, if you had legs sprouting from your sides at 90-degree angles. Clark dumps out what seems to be her entire bag of tricks all at once in “Northern Lights,” and it’s hard to appreciate any one of them when they’re all happening simultaneously.

It’s not until midway through Strange Mercy that the machinery fully kicks in. That’s when Clark unleashes the gorgeous title track, which has the same deliberate, measured approach (and not a few of the sonic strategies) of Kate Bush’s The Sensual World. From that point on, Clark seems like she can do no wrong, even when, for instance, her voice clunks right up against the bottom of her range before the first verse of “Champagne Year” is over. It sounds great on her, vulnerable and calming rather than unnerving and passive. If it also sounds like Jenny Lewis singing “Hallelujah,” Clark still manages to take it in new directions. The same holds true for “Dilettante,” which is like “Bennie And The Jets” with a drier one-two clomp and the closing keyboard freakout transferred to guitar and repositioned to crash through the chorus.

More than anyone, though, it’s Bush that St. Vincent most resembles at this point in her career, even when Clark doesn’t sound like her, or anyone else. When Strange Mercy works, it borders on stunning; when it falters, it’s simply an ambitious whiff. “It’s not a perfect plan,” sings Clark at one point, “but it’s the one we’ve got.”

St. Vincent performs at the 9:30 Club on Nov. 1. $20.