Beautiful Creatures is only the latest example of what happens when one of the many possible rich allegories for adolescent anxiety and alienation gets blown up past the point where it’s possible to care about anyone involved. Based on the first in a novel series by Kami Garcia and Margaret Stohl, it’s set in a small South Carolina town where 17-year-old Ethan Wate (Alden Ehrenreich) has grown disenchanted with everything about the parochial local attitudes. He becomes intrigued with the new girl in town, mysterious Lena Duchannes (Alice Englert), who has moved in with her reclusive uncle Macon (Jeremy Irons). Ethan soon discovers that Lena comes from a family of magical “casters,” and that her impending 16th birthday will mark the moment when her powers will be claimed either by the forces of light or — as she fears, given family history — darkness. It’s perfectly promising to combine Ethan’s sense of being out of place with Lena’s, and writer/director Richard LaGravenese (P.S. I Love You) doesn’t over-complicate the mythology even as he introduces various other family members visiting for Lena’s birthday ceremony. But he’s stranded us with a story that focuses primarily on Lena and Ethan falling in love — an act which, as it turns out, is somehow deeply rooted in the history of Lena’s ancestors. It doesn’t help that the lead actors are a blandly attractive pair, the performances skimming along the surface of whatever real feelings should be part of characters who have known genuine tragedy — aside from whom they’ll go with to the big dance. LaGravanese rarely seems sincere about making them actual people, rather than the latest anonymous stand-ins for viewer fantasies. The more interesting side of Beautiful Creatures is the one that proves far more playful and angst-free. Emma Thompson plays a dual role as both the fire-and-brimstone mother of Ethan’s best friend, and a wicked caster named Sarafine who possesses that body, and chomps into both of them with gleeful abandon. It’s a glorious distraction from the central story when Irons and Thompson — representing Lena’s two possible fates — face one another in the middle of a church for a wonderful ham-off. Combined with Emmy Rossum’s juicy supporting role as Lena’s temptress cousin, it’s hard not to wish that we could all take a detour from the main narrative and just follow these other characters, who seem to be having so much more fun.