A fast-moving cautionary tale about kidnapping. Maggie and Mike are left in charge of four-year-old half-sister Courtenay when their dad and stepmother, Leigh, go on a belated honeymoon; between school bus and school door, Courtenay vanishes. Princeton police consider the usual suspects: the bus driver, both ex-spouses, the local ne'er-do-well who's been making harassing telephone calls to Maggie. Maggie's friends pitch in with projects to fund posters, and a national search is instituted. Dad then confesses that his first wife, Jessica, was a child abuser (she would lock Maggie in a closet in order to get time for herself); in the end, after a fright over another four-year-old found slashed and dead nearby, Courtenay turns up scared but safe. Unstable Jessica has kept her in revenge for losing custody of her own children. Missing children are a well-publicized concern, and, though Martin somewhat exaggerates the danger, her prescriptions for safety are sensible. Her characters are also realistically varied in their response to the crisis, if less surely drawn than in her recent With You and Without You; the antagonism here between Leigh and Maggie lacks a convincing basis, and is too easily resolved. Still, enough suspense to hold readers.