It isn’t much of a stretch to imagine this as a prequel to the pedophile-stalking film Hard Candy, in that it gives us a sense of the traumas that could turn a teenager into a deadly avenger. That film’s star, Ellen Page, here plays Sherry, an American goth girl running amok in Europe, trying anything to identify as a rebel. Running away from home, she encounters Tiger (August Diehl), a handsome guy with a snappy sales pitch about a group known as S.P.A.R.K.—Street People Armed with Radical Knowledge. Sherry joins . . . but soon after, her mom tracks her down and joins too. Initially, everyone suspects a brilliant act of reverse psychology; after all, if your parents think something is cool, it can’t possibly be, right? But Mom is just a little too into it, and it soon appears that she may be an even bigger zealot than Sherry. Writer-director Alison Murray’s story has the no-holds-barred look and feel of a ’70s movie, but her digressions into modern dance are a tad unwelcome.