Fourteen quintillion people treasure the one Joseph Arthur song in their collection. OK, sure, those consumers are mostly under the age of 12, and the Shrek 2 soundtrack is one of only five CDs in their collection, but still, the big green ogre did wonders for J.J. Cale’s career, didn’t he? Peter Gabriel discovered Arthur in the wilds of Akron, Ohio, and, recognizing a kindred songwriter, signed him up like that. Arthur’s music, full of dark secrets, redemption, soul-transforming traumas and enough psychic homicides to fill a Nick Cave record, may be slippery territory for middle schoolers. For a Thursday night close to finals, though, his complicated, murky vision is probably just about right.