Nola has always stood by her younger sister, Song—through surgery, chemotherapy, remission and the recurrence of Song’s cancer—but, craving adventure and normalcy, she takes a summer job as a waitress at Rocky Cove, a swanky Maine resort. On the bus, she immediately bonds with spontaneous, gregarious Carly. When Carly abruptly replaces Nola’s roommate Bridget, Nola is overjoyed, and the two girls spend the first half of the summer as an inseparable duo, known to all as “the Cannolis.” As busy mealtimes in the dining room, lazy days at the beach and beer-soaked parties bleed together, Carly takes over Nola’s life—copying her haircut, becoming pen pals with Song, flirting with the boy Nola likes—undermining Nola’s confidence and sense of self all the while. During a surprise visit from Song, Carly precipitates a dangerous stunt, which prompts a major confrontation with Nola. Carly is ultimately a pitiable figure, and Jacobson’s gradual reveal, through Nola’s first-person, present-tense narration, of the fun, then the danger, of this classic frenemy’s borderline personality disorder is deliciously, palpably tense. (Fiction. 15 & up)