This week, the wunderkind composer Nico Muhly grows up — he tells Kurt Andersen why he chose a crime ripped from the headlines as the story for his new opera. Suzanne Opton captures soldiers at rest between tours in a series of haunting portraits. Plus, a critic assesses Banksy’s month-long art spree in New York City, and designer to the stars Mario Buatta talks high design on the cheap.