This wry, incisive book gathers a well-drawn group of rudderless characters seeking a deeper hold on their world. They’ve drifted far from their true selves — by circumstance (like Ofelio, the lowly but proud migrant worker at the center of ”Diablo”); by their own selfish, stunted conduct (the jealous girl who turns a written homework assignment into a frenzied denunciation of her sister in ”Essay #3: Leda and the Swan”); and by unchecked desire (the itchy dad perturbed to learn that a trip to the pet store won’t yield a peek at his favorite salesgirl in the short, affecting ”Neon Tetra”). The brilliant story ”Mission,” in which a teacher of English as a second language is spurned by a student who misreads his intentions, caps the awe-inspiring debut, Music Through the Floor that introduces readers to Eric Puchner’s great strength: the ability to chronicle the oddest of behaviors with a humane, unsparing voice.