On their most recent release, The Tain (Acuarela), the Decemberists have cast a pall over the relatively sunny pop that’s won the band such a dedicated following over the past two years. The Tain is a five-part, 18-minute song cycle loosely based on a pre-Christian Irish epic, whose young hero, Cuchulainn, turns the tide in a massive cattle raid (or “tain”) on his town of Ulster. In the Decemberists’ version, the tale is muddled, almost abstract, and shorn of its narrative sweep. Kings and warriors fade into the background, and the messiness of birth, sex, and death comes to the fore, colored by lead singer-songwriter Colin Meloy’s rigorous poetic sensibilities: “I will bleed your heart through a samovar soon,” he sings in his nasal voice. (He gets pretty nasty too, describing one character thusly: “She’s a salty little pisser / With your cock in her kisser / But now she’s a will of her own.”) The band makes room for a Kurt Weill-esque waltz similar to its earlier work, but for the most part The Tain’s sound is darker and heavier, tinged with metal, like a chamber version of Dead Meadow; some of the arrangements have a blowsy, world-weary quality reminiscent of Neil Young’s early-70s albums. Fans looking for catchy, off-kilter pop anthems like “Angel, Won’t You Call Me” and “Los Angeles, I’m Yours” may be a bit disappointed by this record, but the Decemberists’ impressive songwriting, musical adventurousness, and exquisitely literate lyrics are all very much intact. Long Winters, Places, and Head of Femur open. $12 in advance, $14 day of show; 18+. Friday, June 4, 9 PM, Metro, 3730 N. Clark; 773-549-0203 or 312-559-1212.