Seventh-grader Callie is a VERY DEEP philosopher, intent on designing her own positive slogan for mugs and T-shirts. The white girl's focus on only happy thoughts becomes difficult when her dad loses his job—the reason for their move to an upscale apartment on the Upper East Side—and she does not have the concert-ticket money promised to a girl at her snobby private school. Stressed, distracted, and late for school after trying to visit her grandma in the titular apartment, Callie decides to skip altogether and finds herself at the Met, a pattern that repeats over several days. On her first day, she meets light-skinned African-American, unschooled Cassius, and together they spend their days in various museums. Just when Callie's cloyingly cute preteen-speak (littered with capitalizations and exclamation points, ew, OMG!) verges on annoying, real issues surface, not only in her family, but to others. As she learns of her grandparents' rejection of her gay uncle, perceives the racism that Cassius experiences, and deals with her younger brother's bully, her character deepens. Cassius reveals that he has Best disease and is going blind; Callie rushes to rescue him when he is lost on the subway. Callie learns about friendship, her family, and the importance of not being stuck in a regret-filled past. As it moves beyond First World problems, this coming-of-age novel reaches a satisfying depth of character and theme. (Fiction. 10-14)