Leigh Stein’s debut novel The Fallback Plan plumbs the Weltschmerz of lost innocence with a splendid mix of seriousness, imagination, and deadpan humor. In the present-day world of quick answers—“What will your life be like in 20 years? Click here to take the quiz and find out!”­ as one of the chapter titles reads—Stein’s narrator reckons with her irreclaimable childhood.