Flippant high-school sleuth Carter Colborn plunges into another mystery, as well as some thorny issues, in this confused, murky story. ""Shut up or else"" says the message attached to the rock that sails through classmate Allison Jones' window. Allison's mother has been vigorously advocating a sex-education course at Dooley High, but until now the negative response has been confined to comments in the hall and letters to the editor; the rock, plus a series of threatening phone calls and several pranks, signals an escalation that draws Carter to the case. With her usual enthusiasm, Carter gathers clues, enters a public-speaking contest, and does research for a newspaper article--all of which allow her (and readers) to review the arguments for and against sex ed in school. Emotions run high--one character declares that AIDS is God's way of punishing ""queers and dopers""--but Carter begins to suspect a different motive behind the attacks, and that Allison herself is the target. Right on both counts--or nearly so: the culprit turns out to be Barrie, a former close friend of Allison's who, impelled by ignorance and fear of being homosexual, is driven to a number of irrational acts, including the harassment and (later) attempted suicide. Barrie is quietly shipped off to a school for troubled teens, while her example convinces the school board to institute the course. Shaw adds touches of comedy in a classical way, by having people jump to conclusions; and, though her own opinions are clear, she gives the opposition room to speak. Still, Barrie is embedded in what is essentially a frothy, Nancy-Drewish story, and cast as an outsider who is more an object lesson than a flesh-and-blood character, her conflict not something for readers to take seriously. A well-paced but superficialtale, its themes inexpertly handled.