Thinner and less inventive than MacLeod's previous, period-setting mysteries (We Dare Not Go A-Hunting, King Devil), this contemporary tale features 16-year-old Persis Green--a gifted pianist with a henpecked father, a monstrous social-climbing mother, and a selfish older sister. So, while the family ignores Persis' artistic promise (she's been offered a master-class scholarship), all attention is focused instead on sister Loni's upcoming marriage to wealthy young Chet Cowles--whose crass parents give Loni a $10,000 diamond/ruby brooch (""a vulgar hunk of ostentation"") as a wedding present. And then the brooch disappears, with Mr. Green, Mrs. Green, and Loni the only possible thieves! Whodunit? The answer isn't surprising--or given much emphasis. Instead, MacLeod focuses her denouement on the Green parents' awakening to Persis' achievement. . . and on Persis' understanding of why her mother (a cartoonishly awful type) is so bossy, superficial, selfish, and insensitive. A subplot--about Loni's disastrous secret date with an old boyfriend--just adds filler. And MacLeod's few attempts at musical detail are embarrassing. (Even many high-school students will know that a piano concerto, by definition, involves an orchestra as well as a soloist.) But, when sticking to light, domestic sitcom, with comic attention to food and clothing, this is a painless little diversion--more for devotees of Bride magazine than mystery/music lovers.