On their sixth studio album, Mogwai reunite with producer Andy Miller, who brings out untold subtleties in their gorgeously moody, instrumental post-rock. The stately “I’m Jim Morrison, I’m Dead” goes from ruminative piano to a crushing, feedback-soaked climax; “Batcat” broods over minor-key riffs with such bass-heavy intensity, it practically scans as sludge metal. And “I Love You, I’m Going to Blow Up Your School” packs all the title’s mystery and drama into pensive guitar/bass interplay that moves like a river toward a waterfall.