Ali's summer starts promisingly enough: away at her grandparents' old lake cottage in Maine, she's babysitting her beloved little cousin, Emma, while her artist aunt paints, and she's planning to uncover the secret her mother's keeping about her childhood at the cottage. She's soon distracted by the annoying Sissy, a local girl who leads little Emma into bratty and dangerous behavior and repeatedly gets Ali into trouble as a consequence, and Ali eventually realizes that Sissy isn't just a persistent kid—she's a ghost. Readers will easily guess Sissy's true identity (she's actually the ghost of a childhood friend of Ali's mother and aunt, who covered up the fact that they were present at her death), and she's too corporeal to be really creepy; the book also winds down rather disappointingly from its fairly early dramatic high point. Hahn is still a polished yarnspinner, though, and there are some intriguing elements here, such as Ali's peer's-eye insight into her mother through Sissy's accounts of their exploits; the book also plays effectively on middle-grade anxieties such as being unfairly blamed and out of one's depth. While this isn't up to the author's classic Wait Till Helen Comes (BCCB 10/86), it's got a compact and approachable shiveriness that would make it an easygoing vacation read.