Katherine Profeta takes Elevator Repair Service’s eloquently understated tactics deeper into dance with 131, which at 45 minutes lasts just about as long as its score, Beethoven’s Quartet in C-sharp Minor, op. 131. Four youngsters hang in a grungy “rec room”: cheap pine-paneled fiberboard, foam soundproofing, linoleum floor, space heater, old sofa, brown fridge-cube, and boombox playing the titular music. The blond hipster (Erik A. Johnson) swigs J&B from a tiny bottle; the hunched-over guy (Nate Schenkkan) reads aloud letters from Beethoven scolding his adopted son, and goes quietly berserk. Shanti Crawford, an impossibly thin, barefoot dancer in sweats (“costumes” by ERS’s Colleen Werthmann) lies on the floor, taking the music into her body; another ERS vet, Susie Sokol, sits and sways, slightly out of sync. They bond and struggle and develop elaborate footwork, inspired by Dance Dance Revolution, to the deep, creamy sound of the strings; they avert a suicide. That’s about all. It’s utterly engrossing, perfectly pitched, and doesn’t miss a beat.